Fill in the blanks.
(a) The slow process of conversion of dead vegetation into coal is called__________.
(b) Coal and petroleum are formed from the dead remains of organisms and are known as __________.
(c) The black thick liquid with __________ smell is known as coal tar.
(d) During the processing of coal to get coke, coal tar and __________ are also obtained.
(e) The process of separating the various constituents of petroleum is known as __________.
(f) Excessive burning of fossil fuels is a major cause of __________.
