Answer:
<u>a. Comma</u>
Explanation:
A clause is a group of words with a subject and a verb. There are two types of clauses: independent (when it expresses a complete thought, and thus, it can stand on its own) and dependent (when it does not express a complete thought).
When a dependent clause comes before the independent clause, the clauses must be separated by a comma. Take a look at the following examples (the dependent clauses are underlined):
<u><em>Even though I loved him,</em></u><em> I had to stop calling him.</em>
<u><em>Since you won't go to the museum either,</em></u><em> I will stay home.</em>
<u><em>After you finish your homework, </em></u><em>go to the kitchen and wash the dishes.</em>
<u><em>When my mom comes home from work, </em></u><em>she sits on the sofa to read books.</em>