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The switch in the circuit shown was on position $a$ for a long time, and is moved to position $b$ at time $t=0$. The current $i(t)$ for $t>0$ is given by

1. $0.2 e^{-125 t} u(t) \; \mathrm{mA}$
2. $20 e^{-1250 t} u(t) \; \mathrm{mA}$
3. $0.2 e^{-1250 t} u(t) \; \mathrm{mA}$
4. $20 e^{-1000 t} u(t) \; \mathrm{mA}$