The answer is (D) because whenever an organic compound burns completely, all of the carbon turns to carbon dioxide and all of the hydrogen turns to water.
Avogadro's law states that the volume of all gases is directly proportional to the moles of gas under constant conditions.
Therefore, the question tells you that the same number of moles of both carbon dioxide and water are formed. However, water contains two moles of hydrogen atoms per mole of water.
Hence, the ratio of moles of carbon to hydrogen in the original compound must be 1:2.
(D) is the only compound with that ratio.
I hope this helps!