why has this proved difficult

why has this proved difficult Why has this proved difficult? 主语是? this 是什么?difficult? Why has this proved difficult?请问这句话的成分,difficult修饰什么词 This medicine has proved effective.中的proved为何是连系动词?为何effective是表语???? 新概念二册52课将答案用括号的词连起.Why has this proved difficult?Do they cover every inch of floor space at the moment or not?(because.which) the article which_______ most useful will be published in this magazineA　provedB has provedC is proved D has been proved为什么是B不是CD His theory___to be true. A.proved B.was proved C.is proved D.has been proved(为什么不用被动,是proved的固定形式吗?） A fact is sth that can be proeved This has proved to be correctproved 到底是怎么用的,第二种是被证明怎么用主动、如果proved是不及物动词那么第一种句子又怎么会成立 He has proved -----for the job,and we are afraid that he'll have to leave this company.AinsufficientB unable Cdeficient As it happened,my advice _____to be wrong.A.proved B.was proved C.has proved D.provesAs it happened,my advice _____to be wrong.A.proved B.was proved C.has proved D.proves 英语翻译Du you find getting up in the morning so difficult that it’s painful?This might be called laziness,but Dr.Kleitman has a newexplanation.He has proved that everyone has a daily energy cycle. she ________herself to be good at typewriting.A.was proved b.has been proved C.proved d.is being proved 为什么选C Theory comes from practice has long been proved.改错 It has been proved that his theory is practical 怎么变为 His theory has been proved ( )如题 The suspicion that the servant is dishonest has proved ____ true.A.all too B.too all C.much too D.too much 选A,why?为什么不选其他选项? ---Why was Professor Wang unhappy recently?---Because the theory he insisted on___wrong.A.proved B.proving C.being proved D.was proved为什么D不对? all this proved that tom was right all this proved tom ___ ____ right.(改为同意句） This is Mr Smith,--------I think has something interesting to tell youwhowhomthat /and why?