Final answer:
The grammatically correct sentence is: 'Even though the boy left early, it does not mean he was sick.' A comma is used to separate the dependent clause from the main clause.
Step-by-step explanation:
The grammatically correct sentence is:
Even though the boy left early, it does not mean he was sick.
In this sentence, a comma is used to separate the dependent clause ('Even though the boy left early') from the main clause ('it does not mean he was sick'). This helps to clarify the structure of the sentence and make it easier to understand. The use of a comma is a standard rule in English grammar for separating dependent clauses from main clauses.