最近遇到一題題目如下
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),我選(d)
我選(d)的原因是覺得while時態應該要跟後面的became一樣,因此選(d)
想請問為什麼答案是(b)
trying要是是當主詞那後面為什麼不需要動詞

原本應該是 while you tried.....,省略成 while tringtrying*

分詞構句，這邊是指主動的狀態。