We owe a lot to the birds and beasts who eat insects but all of them put together kill only a fraction of the number destroyed by spiders. 这句话中、自but开始、后边的那些是句子还是什么?如果是句子,谓语是什么?如果谓语是put和destroyed的话、那only在此相当于and或者or的作用吗?还有、此处destroyed前为什么没有“be”动词?这是被动吗?