It's hard _______ so much work in one day.A.for him doingB.of him doingC.for him to doD.of him to do
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C解析不管of sb.还是for sb.，后面都须用不定式作真正的主语，不能用动名词故排除A和B项。检验不定式前用for sb.还是用of sb.看这个形容词能否作sb.逻辑上的表语,如能作用介词of，否则就要介词for。如本题中hard表示的是”困难”，不能作him逻辑上的表语，我们不能说He is hard，故应用for him to do。