----- Nội dung dịch tự động từ ảnh ----- Read the following passage and mark the letter A, B, C or D to indicate the orrect answer to each of the questions. and In the twentieth century, architects in large cities designed structures a way that reduced noise and yet made living as comfortable as possible. They used such techniques as making walls hollow and filling this all space with materials that absorb noise. Thick carpets and heavy curtains were used to cover floors and windows. Air conditioners and furnaces were designed to filter air throughoundproofing materials. However, after much time and effort had been spent in making buildings less noisy, it was discovered that people also reacted adversely to the lack of sound. Now architects are designing structures which reduce undesirable noise but retain the kind of noise that people seem to need. 28. The word "they" refers to A. architects EM B. cities C. structures D. techniques
