63. According to the passage, branded stations _________.

　　A. spend less money on their gasoline

　　B. have more staff than independent stations

　　C. charge less for high quality oil

　　D. offer a steady oil supply

　　C

　　Ever wonder how much a cloud weighs? What about a hurricane? A meteorologist has done some estimates and the results might surprise you.

　　Let's start with a very simple white puffy cloud — a cumulus cloud（积云）. How much does the water in a cumulus cloud weigh? Peggy LeMone, senior scientist at the National Center for Atmospheric Research in Boulder, Colorado, did the numbers. "The water in the little cloud weighs about 550 tons," she calculates. "Or if you want to convert it to something that might be a little more meaningful … think of elephants."

　　The thought of a hundred elephants-worth of water suspended in the sky begs another question — what keeps it up there?

　　"First of all, the water isn't in elephant sized particles（微粒）, it's in tiny tiny tiny particles," explains LeMone. And those particles float on the warmer air that's rising below. But still, the concept of so much water floating in the sky was surprising even to a meteorologist like LeMone. "I had no idea how much a cloud would weigh, actually, when I started the calculations," she says.

　　So how many elephant units of water are inside a big storm cloud—10 times bigger all the way around than the "puffy" cumulus cloud? Again, LeMone did the numbers: About 200,000 elephants.

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