buaagonggan

AC的错误在于，相比于B，AC两个选项破折号前都不是完整的句子，这不符合破折号的正确用法。

以A为例，Although appearing less appetizing than most of their round and red supermarket cousins, heirloom tomatoes, grown from seeds saved during the previous year- they are....

这里，although后面跟的是状语从句，heirloom tomatoes是主语，grown...是后置定语修饰heirloom tomatoes。所以破折号前的句子主干只有 主语，并不是 主谓（宾）的完整结构，故不符合破折号用法。