While the teacher was explaining the some on the blackboard, the children threw paper aeroplanes

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

While the teacher was explaining the some on the blackboard, the children threw paper aeroplanes around the classroom

around

threw

on the

was explaining

Giải thích

Đáp án : B

Trong khi giáo viên đang giảng, lũ trẻ đang ném giấy gấp máy bay -> 2 hành động: giảng và ném giấy là 2 hành động đồng thời, song song -> cả 2 đều chia ở quá khứ tiếp diễn. B -> were throwing