Less than 35 years after the release of African honeybees outside Sau Paulo, Brazil,their descendants, popular known as killer bees,had migrated as far north as southern Texas. Less than 35 years after the release of African honeybees outside Sau Paulo, Brazil,为什么划线部分可以直接作句中状语?为什么不用在less than 前面加 介词 in呢?想不通了,请NN 不吝赐教。。。