如图是一种新型锁--声纹锁。只要主人说出事先设定的暗语就能把锁打开,别人即使说出暗语也打不开。这种声纹锁辨别声音的主要依据是:
A.音调
B.响度
C.音色
D.声速
答案:C
Only in that way _____ find out how this kind of animal lived and then finished the research on time.[ ]
A. could they
B. they could
C. did they
D. they were able to