Troy Boyd, age 12, of Billings, Mont., for his question:

AFTER THE NILE AND AMAZON, WHICH RIVER IS LONGEST?

The third longest river in the world, and the longest and most important river in China, is the Yangtze River, or the Yangtze Kiang. To most Chinese, the Yangtze is known as the Ch'ang Chiang, or long river.

The Yangtze rises in the Kunlun Mountains of Tibet, 16,000 feet above sea level. The river flows east, southeast and then south into the province of Yunnan. From there it winds in a great double curve and flows northeast across Szechwan Province.

The Yangtze then follows an irregular course east through central China and enters the Yellow Sea 3,424 miles from its source. The river and its branches drain nearly 706,000 square miles.

The Nile River is 5,287 miles long and the Amazon is 4,000 miles long.

Thousands of Chinese live on the Yangtze in boats called junks.

About half of China's ocean trade is distributed over the Yangtze and its branches. Giant ocean steamers travel 680 miles from the coast, while, smaller boats can go 1,000 miles farther inland by way of the Yangtze