It’s a sound you will probably never hear, a sickened tree sending out a distress signal. But a group of scientists has heard
the cries, and they think some insects also hear the trees and are
drawn to them like vultures to a dying animal.

Researchers with the u. s. Department of Agriculture’s Forest (line 5)
Service fastened sensors to the bark of parched trees and
clearly heard distress calls. According to one of the scientists,
most drought-stricken trees transmit their plight in the 50- to 500
kilohertz range. (The unaided human ear can detect no more than
20 kilohertz.) Red oak, maple, white pine, and birch all make (line 10)
slightly different sounds in the form of vibrations at the surface of the wood.
The scientists think that the vibrations are created when
the water columns inside tubes that run the length of the tree break,
a result of too little water flowing through them. These fractured (line 15)
columns send out distinctive vibration patterns. Because some
insects communicate at ultrasonic frequencies, they may pick up the
trees’ vibrations and attack the weakened trees. Researchers are
now running tests with potted trees that have been deprived of
water to see if the sound is what attracts the insects. “Water (line 20)
stressed trees also smell differently from other trees, and they
experience thermal changes, so insects could be responding to
something other than sound,” one scientist said.

24. Which of the following is the main topic of the passage?
(A) The vibrations produced by insects
(B) The mission of the U. S. Forest Service
(C) The effect of insects on trees
(D) The sounds made by distressed trees

25. The word “them” in line 4 refers to ___
(A) trees
(B) scientists
(C) insects
(D) cries

26. The word “parched” in line 6 is closest in meaning to which of the following?
(A) Burned (B) Dehydrated CC) Recovered (D) Fallen

27, The word “plight” in line 8 is closest in meaning to ___
(A) signal
(B) condition
(C) need
(D) agony

28. It can be inferred from the passage that the sounds produced by the trees ___
(A) serve as a form of communication with other trees
(B) are the same no matter what type of tree produces them
(C) cannot be heard by the unaided human ear
(D) fall into the 1-20 kilohertz range

29, The word “fractured” in line 15 is closest in meaning to ___
(A) long
(B) blocked
(C) hollow
(D) broken

30. Which of the following could be considered a cause of the trees’ distress signals?
(A) Torn roots
(B) Attacks by insects
(C) Experiments by scientists
(D) Lack of water

31. In line 17, the phrase “pick up” could best be replaced by which of the following?
(A) Perceive
(B) Lift
(C) Transmit
(D) Attack

32. All of the following are mentioned as possible factors in drawing insects to weakened trees EXCEPT ___
(A) thermal changes
(B) smells
(C) sounds
(D) changes in color

33. It can be inferred that, at the time the passage was written, research concerning the distress signals of trees ___
(A) had been conducted many years earlier
(B) had been unproductive up to then
(C) was continuing
(D) was no longer sponsored by the government