TEST4 Q127
Before _____ to the terms of use, please know that membership is not free, but, we do offer many different membership rates.
(A) agree
(B) agreed
(C) agrees
(D) agreeing
答案：D
疑问有二，如下
1. 是因为前后主词相同所以用D吗？毫无头绪，翻了大全跟怪物讲师也不知道算哪个文法
2. 为何句中的but前后都要用逗点隔开，刚好看到觉得奇怪，顺便问一下
谢谢各位版友

Before V-ingAfter V-ing动名词当介系词的受词 before是介系词 V-ing动名词