21. Various summer camps being available, we can choose _____ based on our own interest.
A. either B. each C. one D. it
22. You can’t catch the charm of English poetry _____ you understand its rhyme.
A. if B. unless C. though D. while
23. —Hurry up! Alice and Sue are waiting for you at the school gate.
—Oh! I thought they _____ without me.
A. went B. are going C. have gone D. had gone
