sentence: People sail in a boat in a river while a man water ski pulling by the boat. sentence:  The person water ski and does a spectacular flip in the air, and continues water skiing. sentence:  Then, the person water ski and flips in the air while two helicopters follows him close. sentence:  After, a man water ski on ramp while an helicopter flies close to him. sentence:  People water ski over a ramp or pulley by a boat.