Mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the following questions.
For the last 20 years, we _________ significant changes in the world of science and technology.
B. have witnessed
D. are witnessing
Answer the question before viewing the answer below
Correct answer: B
Dấu hiệu nhận biết: For the last 20 years => dùng thì hiện tại hoàn thành [ S+have/has + Ved/ V3]