告警根据严重性等级一般分为那些级别（）
A.提示告警
B.主要告警
C.次要告警
D.紧急告警
参考答案：A, B, C, D
The first person was Tony Garcia from Colombia, closely followed by Julia Smith from Britain.
A．to arrive
B．arriving
C．arrived
D．arrives
按钢尺的零点位置，钢尺分为端点尺和（）两种。
