单项选择题
A. Tips are not usually included in the total check. B. A 15 percent tip in large cities indicates satisfactory service. C. People tip waiters and waitresses. D. People always put tips on the table.
A. laser-doppler radar is more accurate than microwave radar B. microwave radar may not ensure absolute precision in measuring varying speeds C. the light-beam radar can measure only slow speeds with accuracy D. microwave radar operates at a higher frequency than laser-doppler radar