问题补充：
— Would you like to share your opinion with us? k+s-5#u
— Ok. Mary is studying harder than before, everyone can see.
A. because
B. which
C. that
D. as
答案：
A. because
B. which
C. that
(答案→)D. as
解析：本题考查定语从句。as和which都可以用来引导非限制性定语从句，它们的先行词是一个句子。在使用时，要注意它们的区别：as从句是说话人对某事的看法、依据、解释或评论等，意为“正如……”。as从句可放在主句的前面、后面或中间。which从句表示某事的状况或结果，它只能放在主句的后面。如：She married him, which was natural.
