Which statement is the converse of the following?
If two angles form a linear pair, then they are supplementary.
A. If two angles are supplementary, then they form a linear pair.
B. If two angles do not form a linear pair, then they are not supplementary.
C. If two angles are not supplementary, then they do not form a linear pair.
D. If two angles form a linear pair, then they are supplementary.