500 Câu trắc nghiệm từ vựng ôn thi THPT QG môn Tiếng Anh có đáp án - Phần 10
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These projects have proved to be very effective in dealing with global climate change, which was considered an insoluble problem in the first 30 years of this century.

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These projects have proved to be very effective in dealing with global climate change, which was considered an insoluble problem in the first 30 years of this century.

hard

challenging

unsolvable

unbearable

Giải thích

Chọn C

insoluble = unsolvable (không thể giải quyết)