I often write ________ letter to my pen friend.

A．a eight hundred words

B．eight hundred words

C．an eight hundred word

D．an eight-hundred-word

上道作业人员应根据需要配备通讯联络工具，作业人员在接到来车报警或通知后，必须停止作业，待列车接近后立刻迅速撤离到安全地带待避车辆。