David is a clever boy and he learned seven languag

问题补充：

David is a clever boy,and he learned seven languages since 1981.那里错了,请说明那里和改正.

答案：

he has learned seven languages since 1981.and连接的前后两个句子一般情况下是保持时态一致的,而且since常用于完成时,所以用has learned而不是learned