请教number和numbers用法 TTGWD9-7

Q7:

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.

1. number of wild salmon have been reduced because of uncontrolled deep-sea and coastal netting
2. number of wild salmon is reduced because deep-sea and coastal netting is not controlled
3. numbers of wild salmon has been reduced because of uncontrolled deep-sea and coastal netting
4. wild salmon’s numbers are reduced by deep-sea and coastal netting that is not controlled
5. wild salmon’s numbers have been reduced by uncontrolled deep-sea and coastal netting

i was dumbfounded that the key offered is E, not B 

偶这样想

B  number of wild salmon is reduced, ( because....)， by.....

                                                           做插入语  

这道题要是选B的话对称的问题怎么办?

后面是 by pollution, and by various other threats to the fish’s habitat.所以前面一定也要有个by引导的,而满足这一点的只有D和E,D比较罗嗦,所以就选E了

我觉得a have错

      b后面的那个is 错

     c numbers错

d 后面的is错

还是没有弄明白 numbers 和 number 的关系 numbers 怎么可以当作“数量”说呢？

我认为应该选B呀！number(数量) is reduced becuase ....is not controlled, by...and by...没有错呀。只不过就是在controlled 和by 之间有个逗号而已呀。 可以给我解释一下吗？ E的numbers 是什么意思?