请教PREP08一道题

葱花kdku

附上原题：
In Scotland, the number of wild salmon have been reduced because of uncontrolled deep-sea and coastal netting, by pollution, and by various other threats to the fish’s habitat.
A.        number of wild salmon have been reduced because of uncontrolled deep-sea and coastal netting,
B.        number of wild salmon is reduced because deep-sea and coastal netting is not controlled,
C.        numbers of wild salmon has been reduced because of uncontrolled deep-sea and coastal netting,
D.        wild salmon’s numbers are reduced by deep-sea and coastal netting that is not controlled,  
E.        wild salmon’s numbers have been reduced by uncontrolled deep-sea and coastal netting,


我的疑问是D和E选项为什么这里的are和have用了复数，明明前面不是the number of要用单数的吗


正确答案是E

葱花kdku

我知道了...