The desert tortoise is found in the Mojave and Sonoran Deserts in North America．It is listed as an endangered species under the United States federal Endangered Species Act and is considered "vulnerable" by the International Union for Conservation of Nature(IUCN)．Despite the laws that protect them，their numbers are still in the decline．

    The desert tortoise in the areas has lived for thousands of years．This animal is able to survive ground temperature over 140 degrees F and is known to live as long as 60 to 80 years．However，ninety-five percent of the life、of a desert tortoise is spent in the ground escaping the heat in a hole or passage in the ground Holes can he easily destroyed by off-highway vehicles that do not say on built roads．Disasters also occur when they seek shade under parked cars．

    Desert tortoises are also harmed by several diseases such as the upper respiratory tract disease often found in adopted tortoises．Pet owners releasing sick tortoises into the wild has resulted in diseases being spread to wild tortoises．

    The desert tortoise feeds on a dune (沙丘) primrose during spring．Non-native Sahara mustard (芥菜) seen in the background is a weed that competes with the native plants for water and nutrients．In some areas，mustard grows so densely that it is nearly impossible for desert tortoises to pass through．Vehicles，which do not stay on built roads and do not get washed frequently，contribute to spreading weeds．

    Rubbish，such as burst balloon，is a danger to desert tortoises．The balloon can be mistaken for food by desert tortoises and，once consumed，may remain in the stomachs and intestines (肠) giving them a false sense of fullness that may cause them to starve．

(1) What does the underlined word "vulnerable" in Paragraph 1 refer to?
A. Hardly noticed． B. Well protected． C. Easily harmed． D. Very useful．
(2) Why does the desert tortoise spend most of its time underground?
A. To escape cross-country vehicles． B. To protect them from the heat． C. To save energy for a long life． D. To shelter them from other animals．
(3) What can we learn about the tortoise?
A. It lives on native plants． B. It promotes the growth of mustard． C. It can fill itself up with burst balloon． D. It digests split balloon easily．
(4) What's the best title of the passage?
A. A Sharp Decline in Tortoise Number B. A Bad Effect Vehicles Has on Tortoise C. Protection of the Desert Tortoise D. Dangers the Desert Tortoise Is Facing