In this task, you're given an article and an answer. Your task is to generate the fill-in-the-blank question for this answer based on the given article. The blanks are always at the end of the question, and can be filled with more than one word or phrase.

Article: Many people have wondered what makes the oceans rise and fall on the word's beaches twice a day. Those tides are caused by the force of the Moon's gravity and the rotation of the Earth. Gravity acts on the center of any solid object. The Earth is mostly molten rock, but compared to the oceans, we can think of it as a solid object. As you know, the oceans are fluid and lie on the surface of the Earth. When the Moon is overhead, the oceans are four thousand miles closer to the Moon than the Earth's center is. Because the oceans are closer, the Moon pulls harder on the water than on the Earth. This stronger pull makes the water bunch up a little under the Moon, creating a high tide. At the same time, the oceans on the opposite side of the Earth are four thousand miles farther from the Moon than the Earth's center is. The Moon's pull on this water is weak. This water bunches up because it is "left behind"(making another high tide) as the Earth is pulled slightly towards the Moon. When the waters bunch up on these two sides of the Earth, they draw water away from the other sides of the Earth, which creates the low tides. As the Earth rotates, different parts of the land and oceans pass through the high-tide and low-tide zones. And that makes the waters on our coasts go up and down.
Answer: Moon's gravity or Earth rotation
According to the passage, there would be no tides if there were no _ .

Article: Read More & Spend Less We have more than 7 million used books for sale, from the earliest board books to the all-time classics. If you like what we have to offer, Tell-a-Friend and we'll give you more reasons to read! Any member of our website who invites friends and family to try our books using the "Tell-a-Friend" program will see a 20% discount when that friend places their first order within 14 days. Start exploring and save big on all your favorites. Here we list some of our books that are heavily discounted. Giraffes Can't Dance By Giles Andreae This book has been pleasing children for over 15 years. Gerald the tall giraffe would love to join in with the other animals at the Jungle Dance, but everyone knows that giraffes can't dance... or can they? 2004, Paperback ISBN:9780439539470 From $0.99 Laugh-Out-Loud Jokes for Kids By Rob Elliott With over 700,000 copies sold, this book will have children rolling on the floor with laughter. A great gift idea for any child. 2010, Paperback ISBN: 9780800788032 From $0.89 Love You Forever By Robert Munsch With simple text and pictures,Love You Foreveris a book to be shared--a story about love that children will carry with them throughout their lives. 1995, Hardback ISBN;9780099266891 FromY=1.98 How to Win Friends & Influence People By Dale Carnegie As the most famous confidence-building book ever published , this classic book will turn your relationships around and improve your relationships with everyone in your life. 2013, Paperback ISBN: 9788087888223 From $0.99
Answer: read more but spend less
The "Tell-a-Friend" program encourages people to _ .

Article: April Fool's Day , was a day of laughing and jokes. This day is kept in many countries, not only in Britain and the USA. This is a day to play jokes and make people laugh. Nobody knows when was the beginning of this custom. Some people connect it with the end of winter and the return of spring which make people merry and ready to play jokes. In Scotland young people were sent for hen's teeth or bird's milk and everybody laughed when they could find such things. In the USA and Britain some people could place a sign on a person's back with the words "push me!" Children often tell a grown-up that his sock is torn or he has something black on his face, and then shout "April Fool!" There is also the old purse trick. A purse is left lying in the street, but when someone wants to take it, it is quickly pulled back by a string which the hidden joker holds in his hand. Or the purse may be filled with stones. Sometimes invitations are sent to people, asking them to come and visit somebody, but when they come they see that nobody expects them. Some people like to telephone to the zoo on the day and ask for Mr. Fish, Miss Fox or Mrs. Cat. All these jokes are very old but still they make people laugh.
Answer: Someone
_ knows when the custom of April Fool's Day started.