as good as 是“和……一样好”的意思,句中as good as后面没有加比较的对象,而是加了逗号跟了一个条件状语if not better than,之后的Anne's本应是接在as good as 后面的,所以加逗号隔开区分.更容易理解的表达是：If my tape-recorder is not better than Anne's,it( my tape-recorder) is as good as Anne's.
再说B选项,如果没有后面的逗号的话,表达是不完整的：缺少as good as 的比较对象~