Given the background: Protozoa generally feed by engulfing and digesting other organisms. As consumers, they have various roles in food chains and webs. Some are predators. They prey upon other single-celled organisms, such as bacteria. In fact, protozoa predators keep many bacterial populations under control. Other protozoa are herbivores. They graze on algae. Still others are decomposers. They consume dead organic matter. There are also parasitic protozoa that live in or on living hosts. For example, the protozoan that causes malaria lives inside a human host. Protozoa are also important food sources for many larger organisms, including insects and worms. and the situation: The students studied two ponds. Class A studied a pond filled with protozoa, while class B studied a pond with almost no protozoa. Answer the following question: Which class observed fewer predator protozoa?
Ans: class B

Given the background: For comparison, sunlight on Saturn is slightly brighter than Earth sunlight at the average sunset or sunrise (see daylight for comparison table). Even on Pluto, the sunlight would still be bright enough to almost match the average living room. To see sunlight as dim as full moonlight on Earth, a distance of about 500 AU (~69 light-hours) is needed; there are only a handful of objects in the Solar System known to orbit farther than such a distance, among them 90377 Sedna and (87269) 2000 OO67. and the situation: John wanted to do a thought experiment. To that end, he started his journey under the full moonlight on Earth. He labeled that as time A. Then he entered his living room. He labeled that as time B. Next he traveled to Saturn. He labeled that as time C. After that, he traveled to Pluto. He labeled that as time D. Then he went to 90377 Sedna. He labeled that as time E. At the end, he returned back to Earth at sunset. He labeled that as time F. Answer the following question: When the light more likely be as bright as time A, time E or time C?
Ans: time E

Given the background: Thermoclines, or sudden changes in temperature. Where the air temperature is higher than the water temperature, shallow water may be warmed by the air and the sunlight but deeper water remains cold resulting in a lowering of temperature as the diver descends. This temperature change may be concentrated over a small vertical interval, when it is called a thermocline.[3][4] Where cold, fresh water enters a warmer sea the fresh water may float over the denser saline water, so the temperature rises as the diver descends.[3] In lakes exposed to geothermal activity, the temperature of the deeper water may be warmer than the surface water. This will usually lead to convection currents.[3] and the situation: Deep lake presents geothermal activity, while Shallow lake has mixing of saline water with fresh water. Deep lake had more instances of divers having problems because of thermoclines. Answer the following question: Which lake has more geothermal activity?
Ans: Deep lake

Given the background: Rain dissolves fertilizer in the soil. Runoff carries it away. The fertilizer ends up in bodies of water, from ponds to oceans. Nitrogen is a fertilizer in the water. Since there is a lot of nitrogen, it causes algae to grow out of control. Pictured below is a pond covered with algae ( Figure below ). Algae use up carbon dioxide in the water. After the algae die, decomposers break down the dead tissue. The decomposers use up all the oxygen in the water. This creates a dead zone. A dead zone is an area in a body of water where nothing grows because there is too little oxygen. There is a large dead zone in the Gulf of Mexico ( Figure below ). The U.S. states outlined on the map have rivers that drain into the Gulf of Mexico. The rivers drain vast agricultural lands. The water carries fertilizer from these areas into the Gulf. and the situation: Two farms were supplying produce to a large city. Green farm used organic methods and no fertilizers, while Bean farm used fertilizer to improve production. Answer the following question: Which farm contributed less to the growth of algae in water?
Ans: Green