TOEFL Reading: ETS-TOEFL阅读机经 - 47N34V7VJ3P96X62L$

According to paragraph 1, all of the following are mentioned as true of the mating calls of frogs EXCEPT A. They can reach frogs in far-off locations. B. They are not blocked by objects of substantial size. C. They are often combined with non-auditory signals. D. They can be received without the frog's needing to orient itself toward the direction of the signal.