【单选题】In the doctor's view,_________
A.
there are both advantages and disadvantages of being rich.
B.
traveling a lot will be beneficial to children.
C.
rich children usually.have little confidence in themselves.
D.
rich kids are often short of money because of their life of luxury.
【简答题】Compare several of the key advantages and disadvantages of observation and survey research.
【简答题】Describe the key advantages associated with the corporate form of organization.
【简答题】设光纤的纤芯折射率n1=1.500,包层折射率n2=1.485。求: (1)相对折射率差Δ; (2)数值孔径NA; (3)入射临界角θmax 。