Which of the following objects is not normally used in current space exploration?
a. space shuttles
c. single use rockets
b. space stations
d. space probes

The last Space Shuttle mission flew in mid-2013.
The surviving shuttles are all in museums now, and
are not used in current space operations.

Note that the US government currently has no way to get
people into or out of space.  When we want to send American
astronauts to the International Space Station, or bring them back,
we rent space on Russian manned space vehicles. 

We pay the Russians somewhat more for these seats that what a
flight to Disneyland would cost you.