(4) ________ rented rooms in a boarding house. Bell was on one floor, and Watson was on another.
Giải thích
4. Do “Bell and his assistant, Thomas Watson” là 2 người => chọnchủngử “they” Chọn D
4. Do “Bell and his assistant, Thomas Watson” là 2 người => chọnchủngử “they” Chọn D