Ifyouwanttokeepyourteethhealthy,you’dbetterbrushthem

问题详情：

If you want to keep your teeth healthy, you’d better brush them ________ twice a day.

A. at least                 B. at once         C. at first             D. for example

【回答】

A

知识点：介词和介词短语

题型：选择题