Answer:
C. parallel phrases.
Explanation:
Parallelism means that the same form of a word is used throughout a particular sentence; for example, only gerunds are used, or only participles, etc. In this case, infinitive phrases are used: to levy war, (to) conclude peace, (to) contract alliances, (to) establish commerce, to do all other... All of these phrases are infinitive, and thus, parallel.
There aren't any clauses in this sentence (it's a simple sentence) and therefore B is incorrect. A doesn't exist in grammar as a term.