如下图所示，小刚早晨7时出门步行到离家6千米远的车站去。返回时骑自行车，上午9时到达家中.

有一边长为4m的正六边形客厅，用边长为50cm的正三角形瓷砖铺满，而需要这种瓷砖（　　）块．

    In the mid-nineteenth century, as iceboxes became increasingly common in American homes, there were efforts to find cheaper and more reliable sources of ice. In the eighteen-thirties, scientists discovered a way to make ice, which is similar to how a refrigerator works. In 1860, there were four artificial-ice plants in the United States; in 1889, there were about two hundred; by 1909, there were two thousand. Ice now came from factories, not ponds, and it was turned out in three-hundred-pound blocks by lowering steel cans of pure water into tanks of refrigerated salted water. Kept below thirty-two degrees, the salted water did not freeze, but the water in the cans did. Those cans were then lifted from the tank, and the ice was taken out of them.

    The ice blocks were delivered to home users, and to the fishing and chemical industries. On the railroads, trains carrying fruit and vegetables had cars at each end filled with blocks of ice. It was a growing industry.

    The great trade began to fall away in the middle years of the twentieth century. The railroad business shrank, and, in the immediate postwar period, block ice lost out to home refrigerators and then to small commercial ice machines. By the nineteen-sixties, things looked very dark. “It was scary,” Dan Ditmar, an ice expert in San Antonito, told me. “Your biggest customers were cafeterias and country clubs, and you'd go out there and they'd say, 'We don't need you anymore; we've got ice machines.'”

    Then the companies that survived the slump（a slump is a period when there is a reduction in business）began investing（投资）in newly developed ice-cube machines, and by the late sixties American ice was becoming a packaged-ice business. And packaged ice was exactly what the country needed. These were years of increased leisure time—more barbecues, more cars, and more houses by the lake. “Things exploded in the nineteen-seventies, Paul Handler said. Ice cubes evolved. They became hugely popular^ shoveled（铲）here and there into picnic coolers and fast-foof sodas. They became noisier.