每星期有四节课。
The process can be divided into four periods.
其演进过程大致可以分为四个时期。
I 've been teaching four periods this morning.
今天上午我已教了四节课。
After that, I have four periods in the morning and four other in the afternoon.
之后，上午有四节课，下午也有四节课。
After that, I have four periods in the morning and four other in the afternoon.
除此以外，我早上和下午都有四节课。
The contract performance covers a 6 month base period with four one-year option periods.
合同日期包括6个月的基本期和四个为期一年的选择期。
Three or four practice periods, each to last a minute or so, will be enough.
一天练习三、四回，每一个只需一分钟左右就够了。
Three or four practice periods, each to last a minute or so, will be enough.
一天练习三、四回，每一个只需一分钟左右就够了。
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