One reason why display rules differ across cultures is because
a.
values and beliefs differ across cultures
b.
some cultures are more evolved than others
c.
certain display rules are more appropriate than others
d.
some cultures do not understand how to show emotions properly

Display rules are social or cultural informal norms that differentiate the ways to be expressed. These are socially and culturally prescribed rules, which people learn through interactions with other people, from the earliest childhood as well as during their lifetime. These are standards of how, when and where emotions should be expressed and to what extent. These standards differ from one culture to another, with regard to all the elements that influenced the creation, development and upgrading of these cultures. Also, it depends on culture, which emotions will be intensified in order to mask the real emotions, for example when they want to conceal grief or dissatisfaction. Culture is defined as common, shared behavior, beliefs, attitudes, values, which are passed on from generation to generation by language or by some other means.  Different cultures cultivate different ideals, and different emotions are used to promote these ideals. For example, in some countries excitement is used as an expression of independence, while others use calmness to express harmony.  

The answer is A.

can you explain it better

the language of nature was a manifestation from god as he said "let there be light" and there was light the world began to assume visible, comprehensible form.

what ever we know now think of the old vision of creation we can be sure that with out the speaking of word -without language- we would have no science today with its striking power to illuminate the world.