When entering a freeway, you must:

Answer: C — Yield to drivers already on the freeway

When entering a freeway, it is important to yield to drivers already on the freeway to ensure a safe merge. Option A is incorrect because it is illegal to drive on the shoulder of a freeway. Option B is incorrect because taking an off-ramp would take you off the freeway, when the question specifically states entering the freeway. Option D is incorrect because the left-most lane is typically reserved for passing and should not be used for merging onto the freeway. By yielding to drivers already on the freeway, you are allowing them to maintain their speed and position while you safely merge into traffic. This helps maintain a smooth flow of traffic and prevents accidents. Therefore, option C is the correct answer.