With sufficient scientific information a manned trip to Mars should be _____.
| A．obtainable | B．potential | C．considerable | D．feasible |
I have reached a point in my life __________ I am sup-posed to make decisions of my own.
| A．which | B．where | C．how | D．why |
Everyone has periods in their lives __________ everything seems very hard.
| A．when | B．where | C．which | D．that |
Gun control is a subject __________ Americans haveargued for a long time.
| A．of which | B．with which | C．about which | D．into which |
—Can you believe I had to pay 30 dollars for a haircut? — You should try the barber's __________ I go. It's only 15.
| A．as | B．which | C．where | D．that |
Occasions are quite rare __________ I have the time tospend a day with my kids.
| A．who | B．which | C．why | D．when |