800 câu trắc nghiệm Điền từ Tiếng Anh có đáp án - Phần 16

These gases combine with the moisture in the atmosphere to (2)______ sulfuric acid and nitric acid. When it rains, these acids dissolve in the rain and turn it acidic. Acid rain is thought to

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These gases combine with the moisture in the atmosphere to (2)______ sulfuric acid and nitric acid. When it rains, these acids dissolve in the rain and turn it acidic. Acid rain is thought to be the worst pollution problem of all.

forms

form

formed

forming

Giải thích

B là đáp án đúng