Tổng hợp đề thi thử tiếng anh thpt quốc gia (Đề số 25)

The doctors hope to _____________ the source of the infection which has been a

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Mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the following questions.

The doctors hope to _____________ the source of the infection which has been a mystery for the medical community since its discovery.

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Giải thích

Chọn D