To understand how these products can be legally promoted to the public,it is necessary to understand

题目

To understand how these products can be legally promoted to the public,it is necessary to understand something of the laws-----------their regulation
A.covering B.covered C.having covered D.having been covered

答案

A 是现在分词作后置定语,表示主动意义,正确.B covered是过去分词,表示被动意义,错误.C.having covered是covering的完成形式,表示该动作先发于understand,这没必要,故错误.D.having been covered是covered这个过去分...