Imperative “必要的,不可避免的；命令的,勢在必行的"像這樣的詞,后面接的句子謂語為“should + 動詞原形”其中,should可以省略.句子結(jié)構(gòu)為：it's imperative that sb + (should)+ 謂語動詞原形+其他成分 eg. 1. It ...It is imperative that this mission don'tfail.那這么說對不對It's essential thatthis mission not fail.be essential that 用虛擬語氣是固定搭配還是這種BE+形容詞+虛擬語氣的句式都是這樣的在主語從句中,謂語動詞的虛擬語氣結(jié)構(gòu)用"should+動詞原形"的結(jié)構(gòu),表示驚奇、不相信、惋惜、理應(yīng)如此等。例如:It is necessary ( appropriate, crucial, desirable,dreadful,essential,important,improper,incredible,indispensable,insistent,natural,preferablepossibleprobableproperrightsignificantsurprisingstrangetragicurgentvital wrong etc.) that we should clean the room every day. It was a pity(a shame,no wonder,etc.) that you should be so careless. It will be desired(suggested,decided,ordered,requested,proposed,etc.)t hat she should finish her homework this afternoon. 在上述三種主語從句中,should意為"應(yīng)該"、"竟然",可以省去,但不可換用為其他形式。