17. She's the woman ............. sister looks after the baby for us
A. who B. which C. that's D. whose
18. A .............. is an enormous system of stars in outer space
A. universe B. solar system C. comet D. galaxy
19. Yuri Gagarin became the first person to eat and drink in ................
A. weightless B. gravity C. specific gravity D. microgravity
20. I passed all my exams- I'm ..........!
A. over the moon B. once in a blue moon C. out of this world D. the sky's the limit
21. Pham Tuan said everything was quite strange he ................when he was on the ground
A. prepared B. has prepared C. had prepared D. prepared