pasagot nman mga pare/mare

Let A={1,3,5,7}, B={2,4,6}, and C={3,6,9}. Find A-C.
{5}
{ }
{1,5,7}
{1}

Which of the following is well-defined?
The set of Happy people
Set of tall people
The set of good writers.
The planets of the solar system

It is the set of all the elements in the universal set (∪) that are not in set A.
Complement set
Intersection of set
Set
Union of set