Which of the following explains Jimmy, the policeman in After Twenty Years, would not arrest his friend in person（）
A. He didn’t recognize the person as a criminal wanted
B. He felt ashamed to arrest his friend
C. He was not feeling good to arrest his once best friend in person
D. He felt scared to arrest his friend
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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
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
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