A tank 36 ft. by 36 ft. by 6 ft. is filled with water to a depth of 5 ft. If a bulkhead is placed in the center of the tank running fore-and-aft along the 36-foot axis，how will the value of the moment of inertia of the free surface be affected?（）

A. The moment of inertia would remain unchanged
B. The moment of inertia would be 1/4 its original value
C. The moment of inertia would be 1/2 the original value
D. None of the above