波长λ=500nm的光垂直照射到缝宽a=0.25mm的单缝,衍射图样中,中央亮条纹两旁第三暗条纹间距离为3mm,则单缝后面透镜的焦距为
A. 25cm
B. 50cm
C. 2.5cm
D. 5cm
睡眠有益于我们的健康。它能帮我们提高记忆力。
A. Sleepingisgoodwithourhealth.Ithelpsusstayhealthyandimproveourmemory.
B. Sleepingisgoodforourhealth.Ithelpsusstayhealthyandimproveourmemory.
C. Sleepingisgoodofourhealth.Ithelpsusstayhealthyandimproveourmemory.
你放学后经常做什么,艾米?
A. Whatdoyouusuallydoafterschool,Amy?
B. Whatdoyouoftendoafterschool,Amy?
C. Whatdoyoualwaysdoafterschool,Amy?
我喜欢待在家里,读书、看电视和听音乐。
A. Ilikestayingathome,toreadbooks,towatchTV,tolistentomusic.
B. Ilikestayingathome,readingbooks,towatchTV,tolistentomusic.
C. Ilikestayingathome,readingbooks,watchingTVandlisteningtomusic.