theresearchscientistsoftenmeetwithproblems_______newtypesofinstrumentsfortheirsolution答案是D
A.require
B.torequire
C.required
D.requiring
为什么是requiring呢?
whatisdonsisdone,itisnouse______anyoneforit
A.blaming
B.blame
C.toblame
D.tobeblaming
为什么?