Two related independent clauses can be joined by a
a) comma
b) comma splice
c) semicolon
d) run-on

c) Semicolon

Explanation:

When the content of two or more independent clauses are closely related, we can join them with a semicolon or coordinating conjunction like “or,” “and,” “but,” “yet” or “so.” If we used a comma instead, a comma splice would occur, which is one of the mistakes made when using a comma incorrectly.

Likewise, a “run-on” is not a possible answer either because it refers to a sentence-error that occurs when two independent clauses are not joined correctly.

which speech are you talking about?

a) he encouraged islamic schools to introduce greek texts.

d) he invited greek scholars to teach their texts to the locals.

explanation: