设f(0)=0,则f(x)在x=0处可导の充要条件为（）
我国从新民主主义进入社会主义的标志是________。
Hefellasleepimmediatelylastnight;hemust________(be)verytired.
Whenhesuddenly________upthesubjectofgeneticengineering,therewasanembarrassedsilence.
Thedirectorrecommendedthatshe________(study)moreEnglishbeforegoingabroad.
