They considered a computer,which was considered a great help in their work．这里该选哪个

题目

They considered a computer,which was considered a great help in their work．这里该选哪个
A．to buy; to be B．buying; being C．to buy; being D．buying; to be

答案

D
consider后面一般加动词ing形式
consider sth （to be）+名词、形容词……
变为被动就成了sth be considered （to be）+名词、形容词……