1. (OG12-11) There are several ways to build solid walls using mud or clay, but the most extensively used method has been the to form the mud or clay into bricks, and, after some preliminary air drying or sun drying, they were laid in the wall in mud mortar.这里为什么用has been?2. 257(GWD6-Q30)正确答案是C,"coyote, because of its amazing ability to adapt to the presence of humans, has been able to expend its" 这个里面because of后面接的东西是不是太多了,wordy不? 3.by using 和using有啥区别啊?