OG15-13题，请教and前为何有逗号

elaineyoung

　　13. There are several ways to build solid walls using just mud or clay, but
the most extensively used method has been the forming of bricks out of mud or
clay, and, after some preliminary air drying or sun drying, they are laid in the
wall in mud mortar.
　　(A) the forming of bricks out of mud or clay, and, after some preliminary
air drying or sun drying, they are laid
　　(B) forming the mud or clay into bricks, and, after some preliminary air
drying or sun drying, to lay them
　　(C) having bricks formed from mud or clay, and, after some preliminary air
drying or sun drying, they were laid
　　(D) to form the mud or clay into bricks, and, after some preliminary air
drying or sun drying, to lay them
　　(E) that bricks were formed from mud or clay, which, after some preliminary
air drying or sun drying, were laid
想问的是，正确答案D中，and前面为什么会有逗号？如果有逗号，不是应该要三个或以上并列，或者and连接句子才可以吗？

elaineyoung

再顶一下 这个问题之前么人解答啊

zbyloveinter

to do sth and to do sth
结构上肯定没问题，这样用逗号应该是方便阅读吧，毕竟后面有一个长长的插入语

你不会应为逗号的问题而选了E吧

elaineyoung

zbyloveinter 发表于 2015-7-19 00:07
to do sth and to do sth
结构上肯定没问题，这样用逗号应该是方便阅读吧，毕竟后面有一个长长的插入语

谢谢，原来是这样。主要也是仔细想想其他选项都太奇怪了…