B．how killer whales communicate with each other

　　C．the reduced population of killer whales caused by whale watching

　　D．hearing problems of the killer whales caused by whale watching

　　解析：选D　主旨大意题。概括文章第一段可得出答案。观鲸船的噪音给虎鲸的信息交流造成了困难。

　　9．Now in a noisy background, the killer whales have to ________.

　　A．sing in a louder voice

　　B．sing longer

　　C．travel in smaller groups

　　D．get nearer to each other

　　解析：选B　细节理解题。由第五段可知，因为受噪音干扰，现在虎鲸"唱"的时间比原来长。

　　10．Scientists believe that killer whales sing to ________.

　　A．warn each other of dangers

　　B．keep in the same group

　　C．send useful information

　　D．enjoy themselves

　　解析：选C　细节理解题。文章倒数第三段有说明，虎鲸"唱歌"是为了交流捕食或繁殖信息。

　　11．From the passage, we can feel that the author is ________.

　　A．angry　　　　　　 　B．hopeful

　　C．worried D．disappointed

　　解析：选C　推理判断题。文章介绍观鲸船的噪音给虎鲸的交流造成了困难，从文章最后的叙述看，虎鲸数量在下降，而科学家也不明白其中原因，因此显然作者对虎鲸的生存状况感到"担忧"。

　　D

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