Reading Comprehension
从下列每篇短文的问题后所给的四个选择项中选出一个最佳答案。

     In the sea, at the base of what scientists call the food chain are single-celled plants. These microscopic algae（海藻）provide the energy for the chain that feeds higher forms of life. Under some conditions, algae suddenly begin to spread very quickly and the event is known as a bloom. Usually blooms are not harmful but some kinds of algae produce poisons. These toxins can be deadly to sea animals and also dangerous to people. When algae bloom, they can change the color of the water as they form dense areas near the surface.
     You may have heard the term "red tide." But experts at the Woods Hole Oceanographic Institute in Massachusetts say this is incorrect. Blooms are not connected with tides and there are not always red. The water can appear brown or greenish. And in fact, some algae can be harmful without changing the color of the water. So instead of red tide, scientists use the term "harmful algal bloom." Algal is the adjective form of alga—a single plant. But they also just say HAB for short.
     The toxins can very quickly kill fish such as herring and anchovies that feed on algae. But even if they survive, they can be dangerous to eat. Not only that, bigger fish that eat the algae eaters may also be dangerous. Some toxins harm only sea life, but others can cause severe stomach and intestinal problems as well as neurological disorders and even death in people. The only way to know whether these toxins are present is through laboratory testing of fish and shellfish.
     Experts say the meaty or hard muscle parts of shrimps, crabs, scallops and lobsters are safe to eat because they do not absorb the poison. But people should not eat the liver or other organs or soft tissues. Also people should not eat other kinds of shellfish during an HAB. These include oysters, clams, mussels and whelks.