[求助]一个语法

oddyuibe

What is much more difficult to determine [U]is/are [/U]the reason for their decoration, the use to which primitive people put the caves, and the meaning of the magnificently depicted animals

这种情况下划线处应该用is 还是用 are 呀

应该看what,还是后面3个并列的名词呀

谢谢

haoyan

Why IS should be used here? Can anyone elaborate?

oddyuibe

嗯，正确答案里用的是is,
这种情况下看前面吗？

Louisa_xy

个人认为应该是is。