The center of gravity of the body is at position in state of unstable equilibrium. 

Highest.

Explanation:

This is because, in a state of unstable equilibrium, the center of gravity is at highest which as a result of when the body topples at it's base, there is a shift in the centre of gravity, and the centre of gravity shift position by moving towards the lower position and it does not return to it's former position again.

.) the observation by semmelweis that more mothers died of childbed fever when their doctors also worked in the morgue

luster is not a good characteristic to use by itself because luster is the property of minerals that indicates how much the surface of a mineral reflects light. the luster of a mineral is affected by the brilliance of the light used to observe the mineral surface.