Learning the definition of retract will help you find the right answer.
http://dictionary.reference.com/browse/retract
Wheels on this type of vehicle can retract
a. a bicycle
b. a station wagon
c. an airplane
d. a sailboat
I feel like I should know the answer to this, but I'm not sure. It can't be a bicycle or a station wagon. So would it be an airplane or a sailboat?
5 answers
A sailboat?
I've never seen wheels on a sailboat.
An airplane?
Right, after a plane gets off the ground, the wheels retract.
1 answer