i confirmed this SC with a native speaker who is the trainner of TOEFL grammar, the following is his reason: only c and d are possible because the subject of "prevented" is "its acoustic energy", therefore "its acoustic energy" should precede the verb or gerund.both a and d ar possible but c is a more efficient structure. and i also prefer C.
[此贴子已经被作者于2007-11-29 16:25:01编辑过] |