I was born ______September 15th, 1998.
A:at
B:on
C:in
Lee is new in Yangzhou. Maybe he needs a _____for sightseeing.
直线P1P2过均匀玻璃球球心O,细光束a、b平行且关于P1P2对称,由空气射入玻璃球的光路如图.a、b光相比( )