it was difficult because of the hard resin____the skin.

问题描述:

it was difficult because of the hard resin____the skin.
1 covered 2 which covering 3 in covering 4 covering
选择哪一个,及分别说出每个为什么对与错

4 covering
because of 这里的of是介词 后面不能跟句子
就用分词形式
如果前面用because,那么后面就得更句子