Final answer:
The appropriate conjunction to complete the given sentence is a subordinate conjunction. The word 'then' could serve as the subordinate conjunction, linking the condition with the consequence.
Step-by-step explanation:
The correct answer to the student's question is C) subordinate. You would use a subordinate conjunction to complete the sentence: "If you're not ready for the bus, then we will have to take a taxi." The word "then" acts as a subordinate conjunction because it connects an independent clause (“we will have to take a taxi”) with a dependent clause (“If you’re not ready for the bus”). Subordinate conjunctions introduce dependent clauses and show the relationship between the dependent clause and the rest of the sentence. In this case, "then" indicates a condition or consequence.