Which of the following bonds is strongest?
Correct option is C. $$-C\equiv C-$$
Carbon-Carbon single bond is also known as a sigma bond. Double bond has one sigma bond and one pi bond whereas a triple bond has one sigma and two pi bonds.
Sigma bond is a strong one. But when we compare three bonds then the triple bond is the strongest followed by double and then single because triple has sigma along with two pi bonds.
Hence the correct answer is option C.