[单选题]
In a first order reaction, the concen9*9ucz yk 1( wxl4 zv;q bhbfwnko0-l+tration [A] of a ,f5lz. :3u cdlup cbm8given reactant can be determined atzd b8cmpf,l:. cu l35u time t, according to the equation below, where [A]$_o$ is the initial concentration of A and k is the rate constant.
ln[A]=-kt+ln[A]$_o$
A. Independent variable
B. Dependent variable
C. y-intercept
D. Gradient