What was the origin of the oil which now drives our motorcars and aircraft? Scientists are confident about the formation of coal, but they do not seem so sure when asked about oil. They think that the oil under the surface of the earth originated in the distant past, and was formed from living things in the sea. Countless billions of small sea creatures and plants lived and sank to the seabed. They were covered with huge deposits of mud and by process of chemistry, pressure and temperature were changed through long ages into what we know as oil. For these creatures to become oil, it was necessary that they should be imprisoned between layers of rock for a great length of time. The statement that oil originated in the sea is confirmed by a glance at a map showing the chief oilfields of the world. Very few of them are far distant from the oceans of today. In some places gas' and oil come up to the surface of the sea from its bed. The rocks in which oil is found are of the marine origin too. They are rocks which were laid down by the action of water on the' bed of the ocean. Almost always the remains of shells, and other proofs of sea life are found close to the oil. A very common sedimentary rock is called shale, which is a soft rock and was obviously formed by being deposited on the seabed. And when there is shale, there is likely to be oil.  There is a lot of luck in drilling for oil The drill may just miss the oil although it is near; on the other hand, it may strike oil at a fairly high level When the drill goes down, it brings up soil. The soil from various depths are examined for. Traces of oil. If they are disappointed at one place, the drillers go to another. Great sums of money have been spent, for example, in the deserts of Egypt, in looking for oil. Sometimes little is found. When we buy a few gallons of petrol for our cars, we pay not only the cost of the petrol, but also part of the cost of the search that is always going on.  There are four main areas of the world where deposits of oil appear. The first is that of the Middle East. Another is the area between North and South America, and a third, between Asia and Australia. The fourth area is the part near the North Pole. When there is no more oil in the present oilfields to bring up, it is possible that this cold region may become the scene of busy oil activity. From the passage, we can infer that   _  .
the North Pole is the largest oil field in the world the Middle East has the finest oil in the main oil areas people haven't opened any oilfield in the North Pole only in oceans can we find oil