Read the following passage and answer the questions given after it.
There are three main groups of oils: animal, vegetable and mineral. Great quantities of animal
oil come from whales, those enormous creatures of the sea which are the largest remaining
animals in the world. To protect the whale from the cold of the Arctic seas, nature has
provided it with a thick covering of fat called blubber. When the whale is killed, the blubber is
stripped off and boiled down. It produces a great quantity of oil which can be made into food
for human consumption. A few other creatures yield oil, but none so much as the whale. The
livers of the cod and the halibut, two kinds of fish, yield nourishing oil. Both cod liver oil and
halibut liver oil are given to sick children and other invalids who need certain vitamins.
Vegetable oil has been known from antiquity. No household can get on without it, for it is used
in cooking. Perfumes may be made from the oils of certain flowers. Soaps are made from
vegetable and animal oils.
To the ordinary man, one kind of oil may be as important as another. But when the politician
or the engineer refers to oil, he almost always means mineral oil, the oil that drives tanks,
aeroplanes and warships, motor-cars and diesel locomotives; the oil that is used to lubricate
all kinds of machinery. This is the oil that has changed the life of the common man. When it is
refined into petrol it is used to drive the internal combustion engine. To it we owe the
existence of the motorcar, which has replaced the private carriage drawn by the horse. To it
we owe the possibility of flying. It has changed the methods of warfare on land and sea. This
kind of oil comes out of the earth. Because it burns well, it is used as fuel and in some ways it
is superior to coal in this respect. Many big ships now burn oil instead of coal. Because it
burns brightly, it is used for illumination; countless homes are still illuminated with oil-burning
lamps. Because it is very slippery, it is used for lubricating the machines.
For engineers which oil is meaningful?