21. As is estimated, more than 20 million shared bikes ______ into operation nationwideby 2025.
A. will have been put B. will have put C. have been put D. will be putting
22. Many Chinese parents are willing to spend money on camp education and study tours for their
children, ______ the industry a booming market with great potential.
A. to make B. making C. having made D. made
23. Many programmers criticized the “996 work schedule”, ______ employees work from 9 am to 9 pm,
6 days a week, with the possibility of ending up in hospital.
A. when B. where C. that D. what
24. Traveling by subway ______ sometimes be quite an adventure, especially during the rush hour.
A. must B. can C. shall D. should
