1)in the fist week of this semester,这学期的第一周2)These books are one week overdue.,这些书超期一周。3)First cleavage cycle,第一次卵裂周期4)first programming cycle,第一个方案周期5)the March issue of the magazine.,这本期刊的第三期6)the 5% damped elastic spectral acceleration at the first period of the structure,结构第一周期谱加速度
