单项选择题

与人鼻咽癌发生相关的病毒是 A. EBV B. HBV C. HCV D. HPV E. HSV

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单项选择题

在简谐波传播过程中，沿传播方向相距为l/2的两点的振动速度必定
A、大小相同，而方向相反
B、大小和方向均相同
C、大小不同，方向相同
D、大小不同，而方向相反

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Off in the distance, you see the headlights of a car, but they are indistinguishable from the single headlight of a motorcycle. Assume the car's headlights are now switched from low beam to high beam so that the light intensity you receive becomes three times greater. What then happens to your ability to resolve the two light sources?( )

A．It remains the same.
B．It becomes one-ninth as good.
C．It increases by a factor of 3.
D．It increases by a factor of 9.