Question

A saturated hydrocarbon is an organic compound which contains hydrogen and carbon joined _____.

Answer 1

by single (sigma) bonds only. No double (pi) bonds are involved.

Answer 2

...by single bonds only.
The term "saturated" implies that no further hydrogen atoms can be added to it. This only occurs when there are no more multiple bonds in the molecule. Whenever there are double or triple bonds (pi bonds), hydrogenation can occur if the pi bonds break and two H atoms attach to each of the C atoms.