Question

obsidian is hard and makes a sharp edge. even though it is brittle.
multiple choice
obsidian is hard and makes a sharp edge. although it is brittle.
obsidian is hard and makes a sharp edge even though it is brittle.
obsidian is hard and makes a sharp edge, although it is brittle
obsidian is hard and makes a sharp edge; even though it is brittle.

Explanation:

The original sentence is a run-on with two independent clauses connected incorrectly. We need to use a comma before the subordinating conjunction "although/even though" when it introduces a dependent clause after an independent clause. "Even though" matches the original conjunction, and the correct punctuation is a comma before it.

Answer:

C. Obsidian is hard and makes a sharp edge, although it is brittle