As You Walk into Your Lounge Room, You Notice That

As you walk into your lounge room, you notice that your roommate is crying. Why is it difficult to know if she is happy or sad?

A) Her facial expressions are likely to be similar.
B) Her physiological reactions are likely to be similar.
C) Her nonverbal cues are likely to be similar.
D) Because it is impossible to pick up on the physiological responses that distinguish happiness from sadness.