Bộ 10 đề ôn thi học sinh giỏi Tiếng anh lớp 9 có lời giải chi tiết (Đề 6)

On the other hand, current research has not yet (59) _______ clear adverse effect associated with the prolonged use of mobile phones.

51/97

On the other hand, current research has not yet (59) _______ clear adverse effect associated with the prolonged use of mobile phones.

created

proved

demonstrated

caused

Giải thích

Chọn B