历史上的楚汉之争的实质是（ ）
A：争夺皇位的战争
B：农民阶级反抗地主阶级的战争
C：刘邦与秦朝之间的战争
D：项羽反抗秦朝统治的战争
It is _______ difficult work that he isn't able to do it _______.
平行用符号____ 表示，直线AB与CD平行，可以记作为____ ．
His erasers are in his ____ (mother) bag.
