你所写的：playing computer games online is not only bad for our eyes but also will waste a lot of time
is要适合not only后面的词,也要适合but also后面的词.
is bad for..没错,但是is will waste...就不对了
所以可以把waste a lot of time改成一个名词：a waste of time
is a waste of time就没有语法错误了