13. My brother ___________ the answer to the question now.
A. know B. knows C. to know D. knowing
14. Where are the ___________ ? On the table
A. childrens’ books B. children books C. books’ children D. children’s books
15. They cant wait___________tomorrow. They must go now.
A. after B. before C. until D. on
16. Listen carefully ___________our teacher, please!
A. with B. to C. for D. in
17. They often go to Ho Chi Minh City___________air.
A. by B. in C. with D. on
18. – ___________ do you visit your hometown? – Once every two or three months.
A. How long B. How often C. How much D. How many
$\text{(+) S + V-(s/es) + …}$