Fill in the banks.
(a) Fossil fuels are ________, ________ and _________.
(b) Process of separation of different constituents from petroleum is called _________.
(c) Least polluting fuel for vehicles is __________.
(a) Fossil fuels are __coal__, __petroleum__ and __natural gas__.
(b) Process of separation of different constituents from petroleum is called __refining__.
(c) Least polluting fuel for vehicles is __compressed natural gas (CNG)__.