As a member of the diplomatic corps, Alex was given special training in the customs, language, and religions of the nonindustrialized country where he would be living. However, Alex probably needed little training to correctly interpret his hosts' expressions of emotion as revealed by their:

The answer is facial expressions.

Explanation:

For decades, scientists have supported the idea that facial expressions are universal. Many studies reveal that gestures like smiling are understood in the same way all around the world. And while it is true that different cultures have slight variations on the same expressions, it shoudln't be a problem to correctly interpret most emotions.