张力式电子围栏平均无故障时间在正常情况下应不小于（）h。
A、5000
B、6000
C、7000
D、8000
参考答案：A
He stayed up too late every night,______ to catch up with his classmates.
A．Having determined
B．being determined
C．determined
D．to determine
乙类传染病
