只要不至于导致误解，且省略的词项可以从主句中获知，则比较分句就可以省略。如果动词的时态不同，则不能省略动词。本句都是一般过去时，did是可以省略的。Nearly as many students sat the art and design exam as the chemistry exam. 剑桥英语语法类似的省略比较分句：More believed that it was genuine than that it was a hoax.