The correct answer is C. Gross total weight of the aircraft/wing area.
Wing loading is a measure of the amount of weight an aircraft’s wings must support per unit of wing area. It is calculated by dividing the aircraft’s gross total weight by the wing area. A high wing loading means that the aircraft’s wings must support a lot of weight, which can make it difficult to take off and land. A low wing loading means that the aircraft’s wings do not have to support as much weight, which makes it easier to take off and land.
Option A is incorrect because it is the load of the wings, not the wing loading. The load of the wings is the total weight of the aircraft that is supported by the wings.
Option B is incorrect because it is the gross total weight of the aircraft divided by the load of the wings. This is not a meaningful measure of wing loading.
Option D is incorrect because it is the gross total weight of the aircraft divided by the total available H.P. of engines. This is not a meaningful measure of wing loading.