46.Since the time humankind started gardening, we _____to make our environment more beautiful.
A.try B. have been trying C. are trying D. will try
47.---Who will go to the station to meet Lorry?
---I will. I her several times before.
A. met B. have met C. had met D. will meet
48. We trees last Sunday. So far we over 3,000 trees there.
A. planted; planted B. planted; have planted
C. have planted; planted D.have planted; have planted
49. By the time you arrive this evening, _____ for two hours.
A. I will study B. I will have been studied
C. I had studied D. I shall have studied
50. No sooner______she entered the house than the telephone rang.
A. has B. had C. have D. having