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题目内容
（石家庄铁道大学-大学英语3）
With the help of high technology, more and more new substances ______ in the past years.
A、 discovered
B、 have discovered
C、 had been discovered
D、 have been discovered
A、 discovered
B、 have discovered
C、 had been discovered
D、 have been discovered
参考答案
