Election and representation

Which of the following statements are incorrect? Identify and correct
them by substituting, adding or rearranging only one word or phrase.
a. FPTP system is followed for all the elections in India.
b. Election Commission does not supervise Panchayat and
Municipal elections.
c. President of India cannot remove an Election Commissioner.
d. Appointment of more than one Election Commissioner in the
Election Commission is mandatory.