Which sentence below is properly punctuated?
a. i am typing a letter, and she is talking on the phone.
b. she finished her work and, then took a long lunch.
c. mae said "why don't you come up and see me sometime? "

a. I am typing a letter, and she is talking on the phone.

Explanation:

Compound sentences consist of at least two independent clauses which can be separated by a comma and a coordinating conjunction, a semicolon or colon.

The rest of the alternatives are incorrect because in sentence B, the comma should precede the coordinating conjunction and; while sentence C contains a quotation which should be introduced by a comma.

A). I am typing a letter, and she is talking on the phone.

Explanation:

The sentence that is appropriately punctuated among the given options is displayed in option A as it employs the correct usage of punctuation marks that offers a clear description about the construction of the sentence and how it should be read. The other two options are incorrect as option B includes a comma after the conjunction which actually should precede it as per the grammatical rule(a comma precede the coordinating conjunctions) while option C does not employ a necessary comma after the clause 'Mae said'. Thus, option A and i.e. 'I am typing a letter, and she is talking on the phone' is the correct answer.

ethos, logos, and pathos.