【单选题】Why did the boy say sorry to the family?
A.
He was late for supper.
B.
He had been away from home all day.
C.
He lost his way on his way home.
【单选题】He had a hamburger for supper this evening,______?
【简答题】当入射光波的类型不同(主要是超声行波和驻波)时,对声光晶体产生折射率变化是不同的,请简述( 1 )行波和驻波的区别?( 2 )当声波为超声驻波时,声光晶体折射率变化情况?
【单选题】He had a hamurger for supper this evening,________?
【判断题】齐次线性方程组基础解系中解的个数s=r(A)