D is the answer to the questions
The answer is Canal. Canals are human-made channels for water movement, or to administration water transport vehicles. In the vernacular, both are alluded to as 'trenches', and as a rule, the built works will have a progression of dams and bolts that make territories of the low-speed current stream. These territories are alluded to as 'slack water levels', frequently just called 'levels'.
In advocating for the League of Nations, Wilson wanted to create a unity between nations in order to avoid the same issues that led to World War I. Unfortunately the US rejected this proposal.
I believe the answer is: positive externality
Positive externality refers to The benefit that enjoyed by a third party when the first and second party are conducting a transaction.
When you receive a vaccines, you prevent yourself from becoming a host that could contaminate other people from getting the virus. In the example above, you and your children are the first and second party. And other children are the third party.
Answers:
1. A successful Union military action
2. <span>Free African Americans were allowed to enlist in the Union army and navy.
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