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 (激光束) on the tiny pieces of algae floating in the water，the researchers said they hear sound waves that tell them the type and amount of contamination (致污物) 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 (光合作用) 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.
The underlined word “algae” in Paragraph 2 probably refers to a kind of________.

A．instrument	B．plant
C．wood	D．pollutant

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.

We can infer from the passage that________.

A．algae can produce a loud sound when polluted

B．algae can die easily from pollution

C．photosynthesis of the algae can only be caused by sunlight

D．photosynthesis of the algae is related to water quality

What would be the best title for the passage?

A．Scientists Listen to Plants to Find Water Pollution

B．A Prototype Tester Is Used to Determine Water Pollution

C．The Importance of Photosynthesis of the Algae

D．The Problem of Chemical and Radioactive Carbon Testing