my sister bought this pair last month .这句话为什么不在时间前面加上介词on

my sister bought this pair last month .这句话为什么不在时间前面加上介词on My sister bought this pair last month.Did she buy them here? 懂英语的请进But my sister bought this pair last month.下面一句是 Did sh 按要求改写句子My sister bought this pair last month.（对划线部分提问,last m 简单的英语问题My sister bought this cake last month不用再last month 前边 My sister bought this pair( last mouth)对打括号部分提问 I bought my shoes this year ;my sister bought hers last year last Saterday前面不加介词,但为什么一定是on the next day off,on my last da my uncle bought a()car last month. this,that,next,last前面为什么不加介词 关于介词短语He bought this pair of shoes in the U.S.last week.1.He This pair of shoes ( )my sister's.