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 _______ has already been pointed out,  grammar is not a set of dead rules.

    A. As            B. It              C. That                 D. Which

 _________ has already been pointed out, grammar is not a set of dead rules.

A. As                       B. It                C. That           D. What

__________ has already been pointed out, grammar is not a set of dead rules.

A. As　　　 　　　　　　　 B. It

C. That　　　 　　　　　　　 D. Which