单选题 .  From good reading we can derive pleasure, companionship, experience, and instruction. A good book may absorb our attention so completely that for the time being we forget our surroundings and even our identity. Reading good books is one of the greatest pleasures in life. It increases our contentment when we are cheerful, and lessens our troubles when we are sad. Whatever may be our main purpose in reading, our contact with good books should never fail to give us enjoyment and satisfaction.
    With a good book in hand we could never be lonely. Whether the characters portrayed are taken from real life or are purely imaginary, they may become our companions and friends. In the pages of books we can walk with the wise and the good of all lands and all times. The people we meet in books may delight us either because they resemble human friends whom we hold dear or because they represent unfamiliar types whom we are glad to welcome as new acquaintances. Our human friends sometimes may bore us, but friends we make in books could never weary us with their company. By turning the pages we can dismiss them without any fear of hurting their feelings. When human friends desert us, good books are always ready to give us friendship, sympathy and encouragement.
    One of the most valuable gifts bestowed by books is experience. Few of us can travel far from home or have a wide range of experiences, but all of us can lead varied lives through the pages of books. Whether we wish to escape from the seemingly dull realities of everyday life or whether we long to visit some far-off place, a book will help us when nothing else can. To travel by book we need no bank account to pay for our way, no airship or ocean liner or streamlined train to transport us, no passport to enter the land of our heart's desire. Through books we may get the thrill of hazardous adventure without danger. We can climb lofty mountains or cross the scorching sands of the desert, all without hardship. Indeed, through books the whole world is ours for the asking. The possibilities of our literary experiences are almost unlimited. The beauties of nature, the enjoyment of music, the treasures of art, the triumphs of architecture, the marvels of engineering, are all open to the wonder and enjoyment of those who read.1.  The main idea of the first paragraph is ______.