Up to now,space  exploring still remainsvery  risky, complex, and expensive endeavor.

Câu hỏi :

Up to now,space  exploring still remainsvery  risky, complex, and expensive endeavor.

A X / a

B the / the

C a / X

D a / the

* Đáp án

A

* Hướng dẫn giải

Phương pháp giải:

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