提升信号发送时必须作到（）。
A、准确
B、清晰
C、可靠
D、无区别
参考答案：A, B, C
It began as just an _______ Monday, but soon became a day I would never forget.
A．ordinary
B．offensive
C．exceptional
D．appropriate
试述喷油泵的泵油原理。
