The correct answer is 4. Being startled is a reflexive action, and waving to a friend is a voluntary action.
Reflexive action occurs involuntarily in a response to a stimulus whereas, a voluntary action is consciously done by a person. The person has total control on the action. A voluntary action is controlled by the brain and involuntary action is controlled by the spinal cord.
Therefore, in the given question, being startled is a reflexive action, and waving to a friend is a voluntary action.