When turning left you:

Answer: B — Yield to oncoming vehicles

When turning left, it is important to yield to oncoming vehicles to avoid causing an accident. Moving into the left lane, while sometimes necessary, should only be done after yielding and ensuring it is safe to do so. Slowing down can also be helpful before turning, but it is not the most important action to take. Ignoring the signal is never a safe option and can result in a traffic violation or accident. Therefore, the correct answer is to yield to oncoming vehicles when turning left.