Comprehension:

Read the given passage and answer the questions that follow.

The beaver had made a dam about hundred yards long, and it had formed out of the quicklyflowing stream, a wide stretch of water about twelve feet deep. The dam was so firm andbroad that it was easy for me to walk along it. After a hundred and fifty yards I came to a'beaver's castle'- a great heap of logs skilfully fitted together, the lower part covered with earthand plants. The upper logs were put loosely together so that the air could pass through to theinterior.In the late autumn, before land and water are covered with snow and ice, the beaver has tomake its dwelling frostproof. It collects young trees and gnaws the stems in a double coneuntil the tree falls.Then the long stems are gnawed into small sections, the thin twigs bitten offand the logs are dragged to the dwelling. There, the timber is piled on the castle, sometimesto a height of ten or twelve feet. Mud is brought up from the bottom of the lake and packedbetween the logs with the animal's clever forepaws. The interior is lined with the finest woodshavings. In this tall shelter, the beaver remains high and dry, and protected from frostthroughout the winter.The only access to the dwelling is under the water, and even the forest wolves are not able topull the firm building apart. The water is the beaver's element. On land it moves slowly andawkwardly. Thus, it is vital for the beaver to have water in which it can swim, and wherenature has not provided this condition for it, it creates it with its dam.The beaver's activities can change whole landscapes. With this dam, for instance, on which Iwas standing, beavers had turned a whole wooded alley into a lake; trees that stood therehad been killed by the water and had disappeared. Aquatic game had settled there. Ducksswam past us, and great must have been the number of fish, as swarms of trout had swumpast me in the clear stream. Wide stretches of meadow had come into existence on thebanks, with flat landing places to which the well-beaten beaver tracks led. Many years ofbuilding, gnawing and dragging must have gone into the completion of this immense task,creating a new region for the beaver to live in.