Which of the following is the main cause of the nonlinear effect of optical fiber（）
A. Fiber ovality
B. Input power of the optical signal
C. Fiber bending
D. Fiber length
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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
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
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