1.（2018北京）—Hi, I’m Peter. Are you new here I haven’t seen you around—Hello, Peter. I’m Bob. I just _________ on Monday.
A.startB.have startedC.startedD.had started
2.（2018北京）_________ we don’t stop climate change, many animals and plants in the world will be gone.
3.（2018北京）_________ along the old Silk Road is an interesting and rewarding experience.
4.（2018北京）Susan had quit her well-paid job and _________ as a volunteer in the neighborhood when I visited her last year.
A.is workingB.was workingC.has workedD.had worked
5.（2018北京）She and her family bicycle to work, _________ helps them keep fit.