This machine needs______once a year in order to work properly求大神帮助A.to check B.checking C.checkD.checked 正确答案是选B,我知道B是被动语态,而且 表示已经做过了.而A和D为什么不行,

This machine is unavailable. This kind of machine can p_______ music. This machine is very easy to This machine is very easy to the machine has been recovered this Machine Machine Machine This is a very expensive machine同义句转换This is( ) ( ) ( ）machine He ordered a washing machine by phone yesterday,and _____ machine will arrive this afternoon. Come and see this machine,Pat and koko. 解释 补充This kind of machine can p___ muice Come and see this machine,Pat and Koko. This machine is used for-----(cut) things into pieces this factory produces machine tools改为被动语态 This machine is ______(easy to undrestand) to ues. who designed this kind of machine?改为被动语态 help~ This machine,______for many years,is still working perfectly.