问题
选择题
One winter day ____, he saw the tracks of animals in the snow and observed that the appearance of each one was different.
A．while he hunting
B．while hunting
C．while he hunt
D．while hunted
答案
答案：B
考查非谓语动词。根据后面的he saw.可知，C项时态不符合要求。While.部分作的是时间状语，A，D项应该为while he hunted ，B，while hunting="while" he hunted