Our factory has been developing rapidly these days This year’s production is five times

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(答案→)A. what
B. that
C. which
D. as
解析：考查从句，做从句时，首先看一下从句是否缺少成份，如果缺少成份，就在关系代词里找；如果不缺少成份，就在关系副词里找，从句it was ten years ago缺少表语，what表示产量，句子意思“我们的厂子这几天一直发展非常快，这一年的产量是十年前的五倍”，所以选A