劳请大神分析一下关于that的省略

minigreen

在OG（第三版） 70题中
The first trenches that were cut into a 500-acre site at Tell Hamoukar. Syria, have yielded strong evidence for centrally administered complex societies in northern regions of the Middle East that were arising simultaneously with but independently of the more celebrated city-states of southern Mesopotamia, in what is now southern Iraq.

(A) that were cut into a 500-acre site at Tell Hamoukar, Syria, have yielded strong evidence for centrally administered complex societies in northern regions of the Middle East that were arising simultaneously with but
(B) that were cut into a 500-acre site at Tell Hamoukar, Syria, yields strong evidence that centrally administered complex societies in northern regions of the Middle East were arising simultaneously with but also
(C) having been cut into a 500-acre site at Tell Hamoukar, Syria, have yielded strong evidence that centrally administered complex societies in northern regions of the Middle East were arising simultaneously but
(D) cut into a 500-acre site at Tell Hamoukar, Syria, yields strong evidence of centrally administered complex societies in northern regions of the Middle East arising simultaneously but also
(E) cut into a 500-acre site at Tell Hamoukar, Syria, have yielded strong evidence that centrally administered complex societies in northern regions of the Middle East arose simultaneously with but

这道题别的选项没有什么问题，
不过OG的解释中提到A选项的that were需要省略，
我的问题就是，1. 究竟什么时候that必须省略，什么时候不能省略。2.在that的省略问题上面gmat的考点是什么呢
^_^

bejamin1111

that were cut into a 500-acre site at THS从句在这里做The first trenches 的定语，这种情况下可以直接用动词的过去分词形式做定语，更加简洁；
that从句做宾语时一般都不应该省略，e.g.
I think [that] you can beat the GMAT.