The chairman thought _____ necessary to invite Professor Smith to speak at the meeting.
A.that
B.it
C.this
D.him
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B解析此题考查学生对it的掌握和运用能力。it作形式宾语,代替后面的不定式to invite Professor Smith to speak at the meeting。that指代前面已发生或者提到的事,或者用于对比作远指代词;this指代将要做的事或用于对比表近指。this和that在句中都有自己明确的意思。