【单选题】I saw the girls _____under the tree when I passed by them. [ ]
【简答题】 什么是产品组合?调整和优化产品组合的主要策略有哪些?
【简答题】一个输入为f(k),输出为y(k)的离散时间LTI系统,已知: (1)若对全部k,f(k)=(-2) k ,则对全部k,有y(k)=0; (2)若对全部k,f(k)=2 -k u(k),有y(k)=δ(k)+a·4 -k u(k),其中a为常数。 求:
【单选题】The research found that more than _____ of girls played with princess toys at least once a week, compared to ____ of boys.
【简答题】一个输入为f(k),输出为y(k)的离散时间LTI系统,已知: (1)若对全部k,f(k)=(-2) k ,则对全部k,有y(k)=0; (2)若对全部k,f(k)=2 -k u(k),有y(k)=δ(k)+a·4 -k u(k),其中a为常数。 求: