最近遇到一题题目如下 Have you ever experienced a dream in which, while ____ to escape from something or someone, you became rooted in the spot? (a)try (b)trying (c)to try (d)tried 答案是(b),我选(d) 我选(d)的原因是觉得while时态应该要跟后面的became一样,因此选(d) 想请问为什么答案是(b) trying要是是当主词那后面为什么不需要动词