Answer:
Square
Explanation:
Given are 3 options with same dimension of 12 feet. The condition is base area should be minimum for maximum volume
A) A hemisphere has

B) A cube with side length 12 ft

C) A cone with diameter 12 ft and height 10 ft

D) A square pyramid

To maxmize the ratio of floor area to volume, we have to maximise the ratio of volume to floor area
Hence of these 4 figures square is the best one that meets the criteria