谓语动词是用is还是用areTwothirdsofthelisteningmaterialsIheardatthebeginningoftheexam____easy.那全校三分之二的学生呢?用单数还是复数?

　　谓语动词是用is还是用are

　　TwothirdsofthelisteningmaterialsIheardatthebeginningoftheexam____easy.

　　那全校三分之二的学生呢?用单数还是复数?