Answer:
A single bond between two carbon atoms consists of a sigma bond. (There are 2 carbon atoms sharing 2 electrons. They are tied together by a sigma bond). A double bond between two carbon atoms consists of a sigma bond and a pi bond. (There are 2 carbon atoms sharing 4 electrons.) A triple bond between two carbon atoms consists of one sigma bond and two pi bonds. (There are 2 carbon atoms sharing 6 electrons).
apex one, two, one, one