Baley and Christian can clean out their lockers after lunch, and they can do their homework tonight. To combine two independent clauses, you have to use a conjunction and a comma.
EXPLANATION :First one is wrong because it should either have a conjunction or use a semicolon instead, two is wrong because colons aren't used to combine sentences, four is wrong because semicolons connect two independent clauses, and "while they do their homework tonight" is a dependent clause because it cannot stand alone as a sentence.
