Answer: {TH, TT, HT, HH } is the sample space.
Explanation:
Since, The sample space is the set of all possible outcomes or results of that experiment.
If a coin is flipped n times then total number of outcomes =

Therefore, When a coin is tossed two times then the total number of the outcomes =
= 4
Thus, the set of the sample space must contains 4 elements.
Therefore, {TH, TT, HT} can not be the set of sample space because it only contains 3 element.
{HH, TT} can not be the set sample space because it only contains 2 element.
{TH, HT} can not be the set sample space because it only contains 2 element.
{TH, TT, HT, HH} is the set of sample space because it contains 4 element.