Scientists in Israel have discovered a new way to test for water pollution by "listening" to what the plants growing in water have to say. By shining a laser beam   on the tiny pieces of _ floating in the water,the researchers said they hear sound waves that tell them the type and amount of contamination   in the water. "It is a red light,telling us that something is beginning to go wrong with the quality of water," said Zvy Dubinsky,an aquatic biologist at Israel's Bar Ilan University."Algae is the first thing to be affected by a change in water quality.""The secret," he said,"is to measure the rate of photosynthesis   in the algae,meaning the plant's ability to transform light into energy." During photosynthesis,plants also release oxygen into the air. Dubinsky's technique is easy to perform because of the overabundance of algae in the planet's water.Most of the oxygen in the atmosphere comes from algae.A prototype tester that occupies about one square meter of a laboratory desktop,shoots a laser beam at water samples to stimulate photosynthesis in the algae.But not all of the laser's heat is used.Depending on the condition of the algae and the rate of photosynthesis,some of the heat is shot back into the water,creating sound waves,Dubinsky said.With a special underwater microphone,researchers are able to analyze the strength of the sound waves and determine the health of the algae and the condition of the surrounding water. "Algae suffering from lead poisoning,like waste discharged from battery and paint manufacturing plants,will produce a different sound than those suffering from lack of iron or exposure to other toxins," said researcher Yulia Pinchasov.She said that testing algae photosynthesis can determine water quality more accurately and easily than laborintensive methods now used like chemical and radioactive carbon testing. Why is the algae tested?
Because it floats on the water. Because it can have photosynthesis. Because it is the first to be polluted. Because it can produce different sounds.
Question: Scientists in Israel have discovered a new way to test for water pollution by "listening" to what the plants growing in water have to say. By shining a laser beam   on the tiny pieces of _ floating in the water,the researchers said they hear sound waves that tell them the type and amount of contamination   in the water. "It is a red light,telling us that something is beginning to go wrong with the quality of water," said Zvy Dubinsky,an aquatic biologist at Israel's Bar Ilan University."Algae is the first thing to be affected by a change in water quality.""The secret," he said,"is to measure the rate of photosynthesis   in the algae,meaning the plant's ability to transform light into energy." During photosynthesis,plants also release oxygen into the air. Dubinsky's technique is easy to perform because of the overabundance of algae in the planet's water.Most of the oxygen in the atmosphere comes from algae.A prototype tester that occupies about one square meter of a laboratory desktop,shoots a laser beam at water samples to stimulate photosynthesis in the algae.But not all of the laser's heat is used.Depending on the condition of the algae and the rate of photosynthesis,some of the heat is shot back into the water,creating sound waves,Dubinsky said.With a special underwater microphone,researchers are able to analyze the strength of the sound waves and determine the health of the algae and the condition of the surrounding water. "Algae suffering from lead poisoning,like waste discharged from battery and paint manufacturing plants,will produce a different sound than those suffering from lack of iron or exposure to other toxins," said researcher Yulia Pinchasov.She said that testing algae photosynthesis can determine water quality more accurately and easily than laborintensive methods now used like chemical and radioactive carbon testing. Why is the algae tested?
A. Because it floats on the water.
B. Because it can have photosynthesis.
C. Because it is the first to be polluted.
D. Because it can produce different sounds.
Answer: