navigation is based on the use of range between navigational satellite and the Information about the satellite’s coordinates is to the user through navigation signal. Range are based on the calculation of the signal time delay compared with the signals by the user equipment. there are four global systems viz., GPS from GLONASS from Russia, Galileo from European and BeiDou from China. In addition, there are regional systems viz., NavIC from India and QZSS Japan. navigation system caters to the users in the world, whereas regional navigation system caters the users in the limited service area. option (d) is the correct answer.