PLANET EARTH Deserts
Winter is the time for breeding. This extraordinary performance is a male Bactrian camel's way of attracting the attention（固定搭配，吸引某人的注意力，attract one’s attention） of a passing female. In summer the camels can't stray far from waterholes. But now, with mouthfuls of snow lying everywhere they can travel widely in search of mates.
Today less than a thousand of these desert specialists remain in the wild. The Gobi, hostile though it is, is their last stronghold（要塞，据点）. There's no other desert quite like the Gobi, but why is this place a desert? There is one simple and massive cause - the Himalayas. Clouds blowing from the south hit this gigantic barrier. As they're forced upwards so they empty their moisture on the mountain slopes, leaving little for the land on the other side.
From the space deserts are very conspicuous（引人注目的）. Dunes（沙丘） of sand hundreds of miles long streak their surface. With no cloak of vegetation to conceal them strange formations are exposed in the naked rock. Africa's Sahara is the largest desert of all. It's the size of the United States and the biggest source of sand and dust in the entire world. Sandstorms like these appear without warning and reduce visibility for days over areas the size of Britain.
