The articles that John has written ……………… difficult to understand.
A. has been
B. was
C. are
D. is
Câu trả lời là: C là đáp án đúng
Công thức nguyên hàm và tích phân
The articles that John has written ……………… difficult to understand.
A. has been
B. was
C. are
D. is
Câu trả lời là: C là đáp án đúng