it is _waste of time for young men to devote themselves to palying computer games on the internet .

题目

it is _waste of time for young men to devote themselves to palying computer games on the internet .
为什么——里要填 "a"阿?

答案

这是一个固定的句型
it is a waste of time for somebody to do sth,
这个最好是要记住,因为很常用