Gunpowder, in some ways the most effective of all the explosive materials, were a mixture of potassium nitrate, charcoal, and sulfur.

Câu hỏi :

Gunpowder, in some ways the most effective of all the explosive materials, were a mixture of potassium nitrate, charcoal, and sulfur.

A. in some ways

B. the most effective

C. all

D. were

* Đáp án

D

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