Answer :
The correct answer is D. Trading favors
Explanation:
An alliance refers to an agreement of reciprocity between different parties, for example, two individuals, organizations or countries. This implies the parties agree on an exchange of certain help, support or favors, for example, countries can agree on protecting each other in war and this means the countries involved need to cooperate and help each other or return the favor if one or more countries have already protected them. Therefore, the reciprocity while being an ally means trading element such as favors or support.