31: he hasn't gone abroad before

32:that computer has been used for three months

33:she won't visit her friends because she does not have time

35:  he asked me how much I thought it would cost 

36 If it doesn't rain tomorrow, we will go camping

37:I have never traveled by air before

38the students are studying for the exam now

39:the weather was so cold that we dicided not to go out

40:the house where we is lived nowis built in the 19 th century

31, he hasn't gone aboard before
32.the computer has been used for three months 
33. she won't visit her friend because she doesn't have time 
34. his speech is considered to be one of the best 

35. he asked me how much I thought it would cost 
36. if it doesn't rain tomorrow , I will go camping
37. I have never travelled by air 
38. the students are studying for the exam now 
39. The weather is so cold that we decide not to go out 
40 . the house where  we are living now was built in 19th century