Being an ally involves reciprocity, which means:
a. getting back at someone when they breach your trust.
b. creating a web of good will that will be there when you need it.
c. making deals behind the scenes.
d. trading favors.

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.

an aneroid barometer is different from a mercury barometer in that it provides readings that increase as air pressure increases.

hope it : )

explanation:

with the profits from the european sales, merchants purchased europe's manufactured  goods, including tools and weapons. then the merchants shipped those manufactured  goods, along with the  american  sugar and rum, to west africa where they were bartered for  slaves.