The correct answer would be:
b. The mandate to marry within one's tribe
In the passage line : "If it had occurred to him that never in the history of his people had a man married a woman who spoke a different tongue, he might have been less optimistic. " It clearly shows how it has never happened that someone in the tribe marries someone form the outside, cause culturally in his tribe the mandate is to marry people from the inside.
The phrase in the parenthesis is acting as an adjective.
You'd have to post the lines to get an answer.
Answer
c alexander the great worked only with green he trusted such as nearchus
