$\int\limits_0^∞[2e^{-x}]dx$, where [.] denotes the greatest integer function, is equal to:

2 ln 4 ln 4 ln 2 None of these

ln 2

$I=\int\limits_{0}^{ln\,2}1.dx+\int\limits_{ln\,2}^{∞}O.dx=ln\,2$