=>

29. D (The invention of the phonograph happened quite by accident...)

30. B (In that laboratory a year later, Edison invented the phonograph while he was trying to iimrove a telegraph repeater)

31. A (In that....while he was trying to improve a telegraph repeater)

32. D (He attached a telephone diaphragm to the needle in the telegraph repeater, in this way, he was able to reproduce a recording that could be played back...)

$\text{@su}$

`29,` `A`

`=>` Dựa vào nội dung bài đọc và phép loại trừ câu trả lời (bài đọc nói chủ yếu về Edison)

`30,` `A`

`=>` Dẫn chứng : Câu đầu tiên đoạn 1 "The invention of the phonograph ... research laboratory."

`31,` `A`

`=>` Dẫn chứng : Câu đầu tiên đoạn 2 "In that laboratory a year later ... telegraph repeater."

`32,` `D`

`=>` Dẫn chứng : Câu thứ 2 của đoạn 2

$\text{@Bulletproof Boy Scout}$