Your answer is

D.) A lot of famous people ride bikes

because of the definiton of extraneous, which is

[irrelavent or unrelated to the subject being dealt with]

A.) is relavent to the essay, because it is dealing with both bikes AND skateboards, and it is COMPARING the two

B.) is relavent, because kids and adults are seen using both, therefore this is COMPARING bikes and skateboards.

C.) is relavent, because it is telling us that bikes have 2 wheels while the skateboard has 4, thereby CONTRASTING them

D.) is irrelavent, because it is neither comparing of contrasting the two, it is just stating something that does not need to be in the essay.

Hope I helped! 🙂