A:①②
B:①④
C:②③
D:②④
—How long ________they_________?—Sorry, I don't know. But I know that Mr. Chen is going to _______a nurse next month.
历史学家一般通过文献记载和出土文物来研究历史,下面能通过文献进行研究的一段历史是( )
____ your clothes ____ very often?