When turning, you should continually give the proper signal:

Answer: D — At least 100 feet before turning

When turning, you should always give a signal before turning to indicate your intention of changing lanes or direction. This is not only for your safety but also for the safety of others on the road. Giving a signal at least 100 feet before turning is the standard practice and it ensures that other drivers have enough time to react and adjust their speed accordingly. It also helps to prevent sudden and unexpected lane changes which could lead to accidents. Choosing option A is incorrect because giving a signal after turning defeats the purpose of communicating your intended action beforehand. Option B is also incorrect as it suggests giving a signal just before turning, which is not enough time for other drivers to react. Option C is also incorrect as giving a signal during turning can be confusing and may not be visible to other drivers. Hence, D is the correct answer.