It's the size of the United States 它的面积相当于美国

47. With no cloak of vegetation to conceal them
    由于没有植被覆盖
48. strange formations are exposed in the naked rock.
    裸露的岩石显露出奇特的造型
49. Africa's Sahara is the largest desert of all.
    非洲的撒哈拉沙漠是世界上最大的沙漠
50. It's the size of the United States
    它的面积相当于美国
51. and the biggest source of sand and dust in the entire world.
    也是全世界最大的沙尘源
52. Sandstorms like these appear without warning
    如此巨大的沙暴出现时毫无征兆
53. and reduce visibility for days over areas the size of Britain.
    所到之处能见度骤降为零 几天内横扫的地区比英国还大

来自《行星地球 第一季 第五集 Planet Earth S01E05 沙漠》第 50 行