Which of the following statements about the numerical aperture （NA） of an optical fiber is incorrect（）
A. The larger the numerical aperture is, the better
B. The smaller the numerical aperture is, the better
C. The value is proportional to the optical fiber’s ability of accepting light
D. It reflects the coupling ability between the light source and the fiber
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Mother solution C of nutrient solution mainly contains______（）
A. iron and trace elements
B. zinc and trace elements
C. magnesium and trace elements
D. copper and trace elements
Common solid medium of soilless cultivation include（）
A. grass charcoal
B. perlite
C. rock wool
D. gravel
Depending on the fact whether the cultivation beds are applicable to solid medium materials, the soilless cultivation is divided into（）and（）
A. hydroponic cultivation
B. soil medium cultivation
C. non-solid medium cultivation
D. aeroponic cultivation
American scientists_showed the necessity of adding trace elements based on the results of experiments, and released the standard formula of nutrient solution accordingly（）
A. Wigman and Boussingault
Boiussingault and Anon
C. Sax and Norbert
D. Hoglaland and Anon
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