Let a={ 6, 7, 8, 9, 10}

then subset of or equal to is a partial order on p(a), the power set of a.

which of the pairs below are not comparable?

a.
( 7, 8, 9} and {8, 9, 10}

b.
{6, 8, 9 } and {6, 7, 8, 9}

c.
{ 6, 7} and {6}

d.
{6, 7, 8, 9, 10} and {6, 10}