Many members ________ were present agreed to the plan.

A.who

D

选择A.who
分析：
Many members是句子的主语，谓语是agreed，宾语是the plan
who were present是修饰members的定语从句，定语从句中需要主语，故whom不能用，which是指物的，也不能用，最后they显然不能用。