Sunil is a student of class VIII at career point in Delhi. During Summer vacations Sunil travelled to Haridwar with his parents. During his journey from Delhi to Haridwar Sunil sat on front seat and his father was driving car. Sunil observed that the road ahead on highway appears to be wet but when the car reaches the spot the road was dry. He inquired this to father but his father told him not to disturb him while driving. In the evening his father explained Sunil that was because of ____.