— .
A：Why not
B：Come back early
C：Good idea
D：Have a good time
频率为6×1014 Hz的激光从S1和S2投射到屏上，若屏上的点P到S1与到S2的路程差为3×10－6 m，那么点P处是亮条纹还是暗条纹？设O为到S1和S2的路程相等的点，则PO间有几条暗纹、几条亮纹？(不含O、P两点处)
For forty years Jane Goodall has been o____ (坦率的) about making the rest of the world understand and respect the life of animals.
