Final answer:
The correct option is to replace the comma after 'microphone' with a semicolon, as it connects two closely related independent clauses. Options 'b' and 'c' are incorrect, as 'b' offers an unnecessary semicolon after a date, and 'c' maintains a comma splice.
Step-by-step explanation:
In addressing the student's question about punctuation, we look specifically at the use of a comma versus a semicolon within a given sentence. The student presents a statement: "In 1878, Thomas Alva Edison invented the carbon microphone, it was used in every telephone until the 1980's." Correct punctuation is crucial to clear written communication, and the proper choice depends on the relationship between the clauses within the sentence.
Option a suggests replacing the comma after 'microphone' with a semicolon. This is the correct modification, as the semicolon can be used to connect two closely related independent clauses which are not joined by a conjunction. Here, "Thomas Alva Edison invented the carbon microphone" and "it was used in every telephone until the 1980's" are both independent clauses that are closely related in content.
Option b is incorrect because the information following the date '1878' is not an independent clause, and therefore does not necessitate a semicolon. Option c, 'no change', is also incorrect because the use of a comma results in a comma splice, an error in English where two independent clauses are joined by just a comma without the appropriate conjunction or punctuation.
Thus, the correct punctuation to use in the student's sentence is a semicolon after 'microphone' to properly connect the two independent clauses.