47. According to paragraph 2, which of the following has made the study of
pheromones difficult?
(A) Pheromones cannot be easily reproduced in chemical laboratories.
(B) Existing technology cannot fully explore the properties of pheromones.
(C) Pheromones are highly volatile.
(D) Pheromone signals are constantly changing.
48. The word "They" in line 24 refers to
(A) pheromones
(B) roles
(C) activities
(D) insects
49. The word "sedentary" in line 29 is closest in meaning to
(A) inactive外语学习网
(B) inefficient
(C) unchangeable
(D) unbalanced
50. Pheromone systems are relatively complex in insects that
(A) also communicate using sight and sound
(B) live underground
(C) prey on other insects
(D) live in organized group
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