▲这个 get as 不是一个固定搭配，它们根本不相干：句中动词 get 的宾语是 who，介词 as 的宾语是 a roommate。句中的 get as 其实是 get…as… 结构，明白了吗？你的句子意思如下：

You never know who you’ll get as a roommate; it’s just a matter of luck. 你无法知道谁会成为你的室友，这完全是碰运气的。

▲下面是几个有趣的句子，对训练句子结构的理解很有帮助，你试试看，注意千万要以为句中的 in in 是固定搭配啊：

This form is to be filled in in ink. 这张表要用钢笔填写。

Tell Mr. Gray to wait: I shall be in in a few moments. 让格雷先生等一等，我一会儿就回来。

He was led in in handcuffs and delivered over to me. 他戴着手铐被带了过来，交到了我手里。

He was talking about having central heating put in. Did he have it put  in in the end? 他那会儿总说要找人装暖气。到底装上了没有？