We always think that it's OK for us to leave our plants home during our vacation as plants won't scream like pets， right？

    A recent study done by a group of scientists at the Tel Aviv University has discovered that some plants will scream when they are under stress．

    The research was carried out on tomato plants and tobacco plants by cutting their stems（茎） and depriving（剥夺） them of water． A microphone was placed 10cm away from them． When their stems were cut， the plants started "screaming" between 20 and 100 kilohertz， and the scientists guess that this scream is probably meant to warn other plants nearby．

    When the tomato plants' stems were cut， 25 ultrasonic（ 超声的） pain sounds were recorded in an hour， and at the same time， 15 ultrasonic pain sounds were recorded from the tobacco plants． When they were deprived of water， the tomato plants recorded even more pain sounds with 35 pain sounds in an hour while the tobacco plants recorded about 11 pain sounds．

    The plants also acted differently to different kinds of stresses． For example， the tobacco plants gave out a stronger "scream"when they were deprived of water than when their stems were cut． But plants that were in no immediate（立刻的） danger gave out less than one ultrasonic sound per hour．

    The group of scientists said that plants are not as quiet as we had always thought， but in fact their voices are so high﹣pitched that we just can't hear them．

    Last year， another study has found out that plants feel pain when they are touched or hurt and they will give of a terrible smell．

（1）What have the group of scientists at the Tel Aviv University discovered？　　

A． Some plants under stress will scream．

B． Plants in danger scream to warn others．

C． Some plants under stress feel energetic．

D． Plants in danger give off a sweet smell．

（2）What was the microphone underlined in paragraph 3 used for？　　

A． Cutting the stems of plants．

B． Depriving plants of water．

C． Collecting ultrasonic sounds．

D． Testing different stresses．

（3）How many ultrasonic pain sounds did the tobacco plants give out in an hour when deprived of water？　　

A． 11．

B． 15．

C． 25．

D． 35．

（4）What can we learn from the passage？　　

A． Tomato plants acted the same under different stresses．

B． Tobacco plants gave off a smell when they were safe．

C． Plants not in immediate danger screamed most weakly．

D． Plants that felt pain screamed loudly for people to hear．