​According to the gate control theory, emotions such as ______ could increase pain by opening the gate, whereas emotions such as _____ could decrease pain by closing the gate.

A) ​happiness; depression
B) ​joy; anxiety
C) ​anxiety; happiness
D) ​depression; anxiety

According to the gate control theory, emotions such as anxiety or stress can increase pain by opening the gate, whereas positive emotions such as happiness or joy can decrease pain by closing the gate. Therefore, choice C is the best option as it correctly identifies the emotion that can increase pain (anxiety) and the emotion that can decrease pain (happiness). The other options either have the wrong pairings of emotions or do not include the appropriate emotions.