Strongest carbon-carbon bond is present in

[Step 1]:
Strength of the carbon-carbon bond increases with increase in number of bonds  between carbon and carbon.
[Step 2]:
In option(1) ${\mathrm{CH}}_3-{\mathrm{CH}}_3$  number of bonds between carbon and carbon is one.
[Step 3]:
In option(2) ${\mathrm{CH}}_2={\mathrm{CH}}_2$ number of bonds between carbon and carbon are two.
[Step 4]:
In option (3)${\mathrm{CH}}_4$  there is no carbon-carbon bonds.
[Step 5]:
In option (4) $\mathrm{HC}\equiv \mathrm{CH}$  number of bonds between carbon and carbon are three.