13．Subway Line 4，__________into use in September 2009，has made traveling in Beijing easier．
| A．having been put | B．putting | C．being put | D．Put |
If you want to find some information about a foreign country, you can ask your friends _______ have been to that country.
| A．whom | B．which | C．who | D．whose |
___________ returning from abroad, he set about setting up a club for young climbers.
| A．Upon | B．At | C．In | D．During |
In his twenties, he took part in sports and gained a great deal of __________.
| A．ability | B．study | C．experience | D．knowledge |
If you want to _________ university, you should work hard.
| A．attend | B．join | C．take part in | D．join in |
The captain commanded that the mission ______ before dark.
| A．must be finished | B．be finished | C．ought to be finished | D．was finished |