能见度用气象光学视程表示。气象光学视程是指白炽灯发出色温为（）的平行光束的光通量，在大气中削弱至初始值的（）所通过的路径长度。
参考答案：2700K;5%
Which of the following statements about the relationship between the value of a callable bond, the value of an option-free bond, and the value of the embedded call option is TRUE（）
A. Value of a callable bond=present value of the interest payments +present value of the principal at maturity.
B. Value of a callable bond=value of an option-free bond + value of an embedded call option.
C. Value of a callable bond=value of an option-free bond-value of an embedded call option.
《危险废物填埋污染控制标准》规定填埋场距飞机场、军事基地的距离应在( )m以上。
A．1000
B．2000
C．3000
D．4000
