问题
选择题
| 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 |
答案
答案：D
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| 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 |
答案：D