An understanding of engineering theories and problem are impossible until

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*Mark the letter A, B. C, or D on your answer sheet to show the underlined part that needs correction in each of the following questions.

An understanding of engineering theories and problem are impossible until basic arithmetic is fully mastered.

engineering theories

are

mastered

Giải thích

Chọn B Ta thấy mệnh đề phía trước chia quá khứ, hai mệnh đề có thời gian liên tiếp nhau, nên mệnh đề sau cũng cần chia quá khứ.

Sửa lại “has gusted” thành “gusted”.