问题：
[单选题]19. 投影器和幻灯机的成像原理基本相同,但对于教师来说投影片是正放的而不是倒放的,这样有利于教师的教学,这是因为投影器增加了( )
A、螺纹透镜
B、平面反射镜
C、新月镜
D、玻璃平台
参考答案：
B
相关内容
- ● 19. 投影器和幻灯机的成像原理基本相同,但对于教师来说投影片是正放的而不是倒放的,这样有利于教师的教学,这是因为投影器增加了( )
- ● CASE OF DEATH OR SERIOUS INJURY TO A PERSON IN AN ACCIDENT OR SHIPPING DISASTER i（）.
- ● Mainly eat 3 or 4 partly cloudy to overcat occaional rain（）lowly outh moderate or good.
- ● （）any cae or upected cae of quarantinable dieae，or any cae of eruptive dieae or any death be dicovered，the local quarantine officer mut be notified immediately．
- ● Should any cae or upected cae of quarantinable dieae，or any cae of eruptive dieae or any death be dicovered，the local Quarantine Officer mut be（）immediately.
- ● Damage to cargo caued by fume or vapor from liquid,gae, or olid i known a（）.
- ● Mater are（）olely reponible for all damage or accident of whatever kind reulting from the navigating or handling of their veel by day or by night.
- ● If he i a common carrier，he i abolutely reponible to the owner of the good carried （）any lo or damage to them unle caued by an Act of God or the Queen’ enemie，or the inherent vice in the good themelve，or the negligence of the owner of the good，or a general average acrifice.
- ● 系统中雷达状态包括Unknown、Operational（or ON）、Failed（or OFF）、Detached。
- ● Owner are to be reponible for lo of or damage to the good or delay in delivery of the good only in cae the lo，damage or delay ha been caued by the improper or negligent towage of the good．Thi mean that（）.
- ● The carrier i liable for lo of or damage to the good or delay in delivery caued by fire，（）the claimant prove that the fire aroe from fault or neglect on the part of the carrier，hi ervant or agent.
- ● Shutdown price（or point，or rule） 停业价格（或停业点、停业原则）
