Giải thích đáp án

Ai giải thích giúp mình câu 48 tại sao k phải là A mà là D ạ
----- Nội dung dịch tự động từ ảnh -----
A. have new coatings been developed
C. development of new coatings
45. Some scientists say it is essential that mankind
A. be reduced
B. reduced
46. She couldn't but
A. stood
47.
A. Knowing not
there crying.
B. standing
48. They received
A. so good
B. new coatings developing
D. new coatings have been developed
C. to stand
where to find the key, the boy could not open the safe.
B. Knew not
C. Not knowing
the amount of air pollution in big cities.
D. will reduce
49. Computers are said to be
A. here to stay
C. here and there
50. "She's the best pianist in the school."
C. reduce
for the development of mankind.
D. stand
advice from their parents that they became successful.
B. such a good
C. so good an
D. such good
D. Didn't know
B. neither here nor there
D. here today, gone tomorrow
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