Explanation
Correct answer: C.
Choice C is the best answer. The convention being tested is the use of punctuation within a sentence. This choice correctly uses a comma to mark the boundary between the introductory participial phrase ("Hoping…classroom") and the main clause ("Huerta…farmworkers").
Why the other choices are wrong
Choice A
Choice A is incorrect because it results in a rhetorically unacceptable sentence fragment beginning with "hoping."
Choice B
Choice B is incorrect because a semicolon can’t be used in this way to mark the boundary between the participial phrase ("Hoping…classroom") and the main clause ("Huerta…farmworkers").
Choice D
Choice D is incorrect because it fails to mark the boundary between the participial phrase ("Hoping…classroom") and the main clause ("Huerta…farmworkers").