While______ the article, I was wondering whether e-books would replace print books soon.
A. reading
B. read
C. was reading
D. to read
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It was not until the 1990s______ industrial robots became really cheap.
A. which
B. who
C. whom
D. that
He was an English teacher before ______ here.
A. coming
B. come
C. comes
D. came
Would you like ______ me a favor?
A. doing
B. to do
C. did
D. does
Sometimes I like to go ______ with my brother.
A. swim
B. swam
C. swimming
D. swims
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