Density is also an important physical property of matter. The concept of density combines what we know about an objects mass and volume. Density reflects how closely packed the particles of matter are. When particles are packed together more tightly, matter is more dense. Differences in density of matter explain many phenomena. It explains why helium balloons rise. It explains why currents such as the Gulf Stream flow through the oceans. It explains why some things float in or sink. You can see this in action by pouring vegetable oil into water. You can see a colorful demonstration in this video.

Question: "What are three examples of density given in the article?"

OPTIONS:
- no
- yes

Answer: "Gulf Stream flow through the oceans"

Response: yes

Little is known of the earliest Stone Age inhabitants of Europe's southwestern extremity. The ancient Greeks called them the Cynetes (or Cunetes). Whatever their origins, their culture evolved under the pressure and influence of foreign forces. Among the many invading armies that settled here and contributed to nascent Portuguese culture were Phoenicians, who settled in the area around 1,000 b.c., followed by the Celts, Iberians, Greeks, and Carthaginians. But it was the Romans, who arrived late in the third century b.c., who most greatly influenced all of Iberia. They built towns, industries, roads, and bridges, developed agriculture, and bequeathed the Latin language, of which Portuguese is a direct descendant. The Romans named the southwestern province of the peninsula Lusitania, oddly enough for one of the Celtiberian tribes they defeated, and by the third century a.d. had introduced Christianity. By the beginning of the fourth century the Algarve had a bishop in place, based in Faro. But Rome had already fallen into decay, and soon hordes of northern tribesmen took over the empire. The Algarve fell to the Visigoths in the mid-fifth century. Under Moorish Rule In a.d. 711, the Moors brought powerful armies from North Africa and launched a devastating attack on the Iberian peninsula, conquering much of what would become Spain and Portugal. They imposed Islam and left an indelible influence on the countryside and the population of the Algarve. The Moorish legacy can still be seen in the form of wells and waterwheels, squat white houses, the dark complexions of the people, and in the very name given the regiontaken from Al-Gharb, which means "country of the west" (when the Moors conquered the territory, it was the most westerly in the known world). The Moors governed their Iberian kingdoms from across the border in Seville, but the Algarve had its own regional capital and huge, invulnerable fortress. The capital was Chelb (or Xelb), and it was bigger and better defended than Lisbon. Today the town, known as Silves, is a provincial outpost whose only besiegers are busloads of tourists who climb the narrow streets up to the old Moorish ramparts.

Question: "What was the Portuguese city of Silves was once known as?"

OPTIONS:
- no
- yes

Answer: "Xelb"

Response: yes

Tom's relaxation at the beach is interrupted by Jerry who inadvertently walks all over a sunbathing Tom going fishing . Jerry falls into Tom's mouth and while escaping , nearly causes Tom to swallow his beach towel . Jerry goes out to the pier and casts his favorite bait : cheese . Tom pulls on the line and makes Jerry reel him in . Jerry lets go of the line and Tom struggles to stay afloat , losing the string . Tom barely catches the pier , but Jerry swings the pole at him . After a few misses , Jerry whistles and then lands a direct hit . He runs to the end of the pier and pulls off the end board . Tom ca n't brake , and walks the plank until Jerry pulls it out , causing Tom to fall into the water and without emerging . A drowning Tom wakes up on the sea bed , where he finds himself still alive . He starts imitating the majestic sea creatures until he spots Jerry . The cat grabs him , but Jerry pulls away revealing that he has become a mer-mouse . Jerry swims in circles until Tom's head has done a 360 , and is then grabbed again . Jerry slaps Tom face with his tail , then spins his ears in to the shape of a wrench . The cat gives chase through shipwreck windows until Tom hangs back to swallow the mouse . Jerry breaks out through Tom's left eardrum . Jerry hides and disguises himself as a seahorse to join a father seahorse leading his babies , fooling the cat for only a while . Jerry then gets lassoed and captured , but Tom gets tricked into holding a fishing line and is caught .

Question: "When does Tom almost drown?"

OPTIONS:
- no
- yes

Answer: "Tom looses the string"

Response: yes

In February 1998, the 40-year-old Saudi exile Usama Bin Laden and a fugitive Egyptian physician, Ayman al Zawahiri, arranged from their Afghan headquarters for an Arabic newspaper in London to publish what they termed a fatwa issued in the name of a "World Islamic Front." A fatwa is normally an interpretation of Islamic law by a respected Islamic authority, but neither Bin Laden, Zawahiri, nor the three others who signed this statement were scholars of Islamic law. Claiming that America had declared war against God and his messenger, they called for the murder of any American, anywhere on earth, as the "individual duty for every Muslim who can do it in any country in which it is possible to do it." Three months later, when interviewed in Afghanistan by ABC-TV, Bin Laden enlarged on these themes. He claimed it was more important for Muslims to kill Americans than to kill other infidels." It is far better for anyone to kill a single American soldier than to squander his efforts on other activities," he said. Asked whether he approved of terrorism and of attacks on civilians, he replied:"We believe that the worst thieves in the world today and the worst terrorists are the Americans. Nothing could stop you except perhaps retaliation in kind. We do not have to differentiate between military or civilian. As far as we are concerned, they are all targets." Note: Islamic names often do not follow the Western practice of the consistent use of surnames. Given the variety of names we mention, we chose to refer to individuals by the last word in the names by which they are known: Nawaf al Hazmi as Hazmi, for instance, omitting the article "al" that would be part of their name in their own societies. We generally make an exception for the more familiar English usage of "Bin" as part of a last name, as in Bin Laden. Further, there is no universally accepted way to transliterate Arabic words and names into English. We have relied on a mix of common sense, the sound of the name in Arabic, and common usage in source materials, the press, or government documents. When we quote from a source document, we use its transliteration, e.g.,"al Qida" instead of al Qaeda. Though novel for its open endorsement of indiscriminate killing, Bin Laden's 1998 declaration was only the latest in the long series of his public and private calls since 1992 that singled out the United States for attack. In August 1996, Bin Laden had issued his own self-styled fatwa calling on Muslims to drive American soldiers out of Saudi Arabia.

Question: "The fatwa that Bin Laden and Ayman al Zawahiri arranged to published, what was the matter with it?"

OPTIONS:
- no
- yes

Answer: "Several pages were omitted"

Response:
no