Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct word or phrase that best fits each of the numbered blanks from 26 to 30. T...

* Hướng dẫn giải

Kiến thức: đại từ quan hệ 

• “parents” là danh từ chỉ người  chọn “who”

Presumably, most parents (27) _________ are always worrying about their children's safety buy mobile phones for them to track their whereabouts. 

 Chọn đáp án B