21. Stephen Hawking died on March 14, 2018 which sparked both worldwide mourning and a _______ of his life’s achievements.
A. conservation B. reservation C. preservation D. celebration
22. It is almost five years since Jimmy taught high school students and he _____ as an interpreter in a foreign enterprise.
A. served B. had served C. is serving D. would serve
23. When asked whether the information on the Internet is true or false,____they were not sure.
A. half of whom said B. half of them saying
C. half of them said D. half of whom saying
