题目列表(包括答案和解析)
15. Researchers _______ to develop vaccines and this will probably take several months to complete.
A. are working B. worked C. will work D. has worked
Researchers _______ to develop vaccines and this will probably take several months to complete.
A. are working B. worked C. will work D. has worked
15. Researchers _______ to develop vaccines and this will probably take several months to complete.
| A．are working | B．worked | C．will work | D．has worked |
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