Although the Ar camel, or dromedary, can go without drinking for a long while, its hump(驼峰) does not store water as is commonly believed. The real 【B1】______ of the animal’’s unusual ability to store water 【B2】______ in the fact that very 【B3】______ of the camel’’s water is lost by 【B4】______ through the skin. Instead of 【B5】______ out great quantities of water, the camel’’s body temperature 【B6】______, sometimes as much as eleven degree, to compensate 【B7】______ external heat. When a camel 【B8】______ require water, it replaces only the 【B9】______ lost since its last drink. In Egypt, 【B10】______ November and April, the camel 【B11】______ go for three or four months without drinking if it 【B12】______ in lush(繁茂的) pastures where dew(露水) and 【B13】______ keep the vegetation green. If only 【B14】 ______ feed is available, the camel will get 【B15】______ after several weeks—even during January. The 【B16】______ of time a camel can go without drinking is greatly 【B17】______ by time of year, force of wind, heat in the air, 【B18】______ of sunlight, amount of the 【B19】______ carried, speed that animal travels, and number of hours spent daily 【B20】______ travel.

A．shall
B．must
C．can
D．may