问题
选择题
At the beginning of class, the noise of desks __________ could be heard outside the classroom.
A．opened and closed
B．to be opened and closed
C．being opened and closed
D．to open and close
答案
C。
由于是用于介词of后作宾语，所以要用动名词，不用不定式或过去分词，故选C。另外，由于desks与open和close的关系是被动关系，故要用动名词的被动式being opened and closed。