David Talbot, age 10, of Willingboro, N.J., for his question:

HOW LARGE DOES A YAK GROW?

A yak is a wild ox of Asia that you find in many zoos. The animal stands over six feet at the shoulders but it carries its head low most of the time, with its nose almost touching the ground. The yak may weigh as much as 1,200 pounds.

The yak is agile in spite of its bulk and heavy forequarters. It can slide down icy slopes, swim swift rivers and cross steep rock slides. If forced to defend itself, it charges furiously.

Excessive hunting has resulted in the killing of so many wild yaks that the animal is now in danger of extinction, the experts tell us.

The domestic yak, often called the grunting ox, is the result of many generations of careful breeding. It is used as a pack animal in Tibet and can carry a heavy load 20 miles a day.

The domestic yak also provides food. Its milk is rich and its flesh is regularly dried or roasted for food.