Final answer:
Two sentences correctly follow coordination and subordination rules by using 'and' and 'but' as coordinating conjunctions to combine independent clauses. One sentence that attempts to use 'however' is improperly punctuated and does not correctly coordinate the two clauses.
Step-by-step explanation:
The sentences that follow the rules of coordination and subordination correctly balance the relationship between independent and dependent clauses, and use punctuation to reflect those relationships.
"As Clark Kent, he spends his time writing for the Daily Planet, and as Superman, he spends his time saving humanity." This sentence correctly uses the coordinating conjunction 'and' to join two independent clauses that are equally important.
"As Clark Kent, he spends his time writing for the Daily Planet but, as Superman, he spends his time saving humanity." Here, the coordinating conjunction 'but' is correctly used to contrast two independent clauses.
The sentence "As Clark Kent, he spends his time writing for the Daily Planet, however, as Superman, he spends his time saving humanity." is incorrectly punctuated as it employs 'however' as a bridge between two independent clauses without the proper use of a semicolon or period before 'however.'