Border checkpoints have been upheld: a. on the nation’s waterways. b. at international borders. c. at checkpoints well inside the nation’s borders. d. all of the above.

d. All of the above

Explanation:

Border check point are recognized in every place that has an access between either two cities or town, this could be land, sea, then that of air. When border check point are upheld they affect;

•The nation's waterways

•International borders.

•Checkpoints well inside the nation's boarders.

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