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

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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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大学英语三级A级

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