一、单句语法填空
1.Silk          (become) one of the primary goods traded along the Silk Road by about 100 BCE. 
2.When walking down the street,I came across David,whom I           (not see) for years. 
3.Just as I got to the school gate,I                                                   (realise) I had left my bag in the cafe.
4.Jack          (work) in the lab when the power cut occurred. 
5.I went to Ningxia and       (stay) there for one year,teaching as a volunteer. 
6.Sofia looked around at all the faces; she had the impression that she        (see) most of the guests before. 
7.During his stay in Xi’an,Jerry tried almost all the local foods his friends          (recommend). 
8.She          (phone) someone,so I nodded to her and went away. 
9.I found the lecture hard to follow because it          (start) when I arrived. 
10.The twins,who           (finish) their homework,were allowed to play badminton on the playground. 
11.Writing out all the invitations by hand was more time-consuming than we           (expect). 
12.Oh,no!We’re too late.The train         (leave). 
13.I felt very tired when I got home,and I      (go) straight to bed. 
14.He was unhappy when he sold his guitar.After all,he      (has) it for a very long time. 
15.I’m calling about the apartment you    (advertise) the other day.Could you tell me more about it?