Explanation:

2nd option is correct.
The construction of double dome in Islamic architecture was first experimented by Sikander Lodi.
A double dome is built of two layers. There is one layer inside which provides ceiling to the interior of the building. The other layer is the outer one which crowns the buildings. The devices of double dome enable the ceiling inside to be placed lower and In better relation to the Interior space it covers. This is done without disturbing the proportions and the effect of elevation of the exterior. The method of making double dome was practised In east Asia for quite sometime before it was imported into India.