A man and a woman stand in front of a Christmas tree contemplating a single thought.
Two people stand lost in thought in front of a tree.
If a man and a woman stand in front of a tree contemplating a thought, then it is safe to say two people stand lost in thought in front of a tree, because a man is a person, and a woman is a person. Together they are two people. They are both thinking, and they are both standing in front of the tree.
People are in front of a Christmas tree.
A man and a woman are two people.