严禁在重要空白凭证上（）空白重要凭证。
A.预先加盖印章
B.严禁跳号发售
C.严禁跳号使用
D.严禁购买
参考答案：A, B, C
抛物线y2=4x的焦点F的坐标为______，点F到双曲线x2-y2=1的渐近线的距离为______．
—Why are you walking to school?
—Because my ______ is broken.[ ]
A. radio
B. watch
C. bike
D. bag
