______ the Internet of Things is to become a reality, its developers should pay more attention to its security.
A. If
B. Although
C. Until
D. Unless
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Unlike many companies______ service stops once the sale is made, our service begins once you buy our product.
A. what
B. whose
C. that
D. which
While______ the article, I was wondering whether e-books would replace print books soon.
A. reading
B. read
C. was reading
D. to read
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