About 15 years ago, scientists did many experiments (develop) _____ the tools to

游客2023-09-25  24

问题 About 15 years ago, scientists did many experiments (develop) _____ the tools to detect new planets.

选项

答案 to develop

解析 本题考查动词不定式。do sth.to do“为了……做某事”。
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