Answer: Option A; car ahead of you is turning
Step-by-step explanation: When a car ahead of you is turning, you need to stay in your lane itself, otherwise it will disturb the vehicles coming behind you.
Also, when traffic is coming in your lane, you can change lanes which are less crowded, so that the vehicles get space to move and less traffic accumulates. That's why option B is incorrect. You need to change the lane because lane beside center should be kept free for cars behind you to overtake, that's why option C is also wrong.