题目：
1.Betty's grade is good.
2.Ben's grade is very good.
(以Betty's grade为句首，用比较级合并句子)
拟答如下3种是否都可以？哪句最好？
1.Betty's grade is less good than Ben's.
2.Betty's grade is worse than Ben's.
3.Betty's grade is not better than Ben's.

Betty's grade is not as good as Ben's.