What does the passage mainly discuss? According to paragraph 2, which of the following has made the study of pheromones diffic

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问题 What does the passage mainly discuss?
According to paragraph 2, which of the following has made the study of pheromones difficult?

选项 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.