First, we must understand why the three other choices are not mixtures. Salt is a compound made from elements Sodium and Chlorine. Aluminum is an element. Carbon dioxide is also a compound composed of Carbon and Oxygen.
Now, gasoline. is substance made from refined crude oils (or hydrocarbons). As a matter of fact, gasoline is an example of a homogenous mixture.
Thus, amongst the choices, the mixture would be gasoline.
