Did you read a book about customs last week?-- Yes, I found very useful to know the c

-- Did you read a book about customs last week?
-- Yes, I found very useful to know the customs of foreign countries.
A. that
B. this
C. it’s
D. it

A. thatB. thisC. it’s(答案→)D. it解析：句意：上周你读了一本关于风俗的书吗？是的，我发现了解外国的风俗习惯非常有用。Find + 名词 + 形容词，是find的一种习惯用法，其中名词作宾语，形容词作宾补。此句中to know the customs of foreign countries是真实宾语，为了使得句子结构平衡，就将其放在了后面，让it来代替它充当宾语。所以选D。

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