Mark the letter A, B, C, or D on your answer sheet to indicate the cor

Mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the following questions.    

Researchers are developing low-cost devices. These devices can detect water pollutants in rivers and lakes.

• A. A. Researchers are developing low-cost devices that can detect water pollutants in rivers and lakes.
• B. B. Researchers are developing low-cost devices to detect water pollutants in rivers and lakes.
• C. C. Researchers are developing low-cost devices so that they can detect water pollutants in rivers and lakes.
• D. D. Researchers are developing low-cost devices who can detect water pollutants in rivers and lakes.

A; nối 2 câu bằng đại từ quan hệ that thay thế cho vật (low-cost devices) -> đúng
B: "to" nối 2 câu thể hiện mục đích -> câu gốc không thể hiện mối quan hệ này
C: "they" thay thế cho researchers -> sai nghĩa so với câu gốc
D: đại từ quan hệ "who" chỉ thay thế cho người -> sai