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The solution of $X=A(t) X(t)$, is

1. $e^{\mathrm{At}} \cdot \mathrm{X}_{0}$
2. $e^{\int_{t_{11}}^{\prime} A(\tau) d \tau}, X_{0}$
3. $\left[I+\int_{t_{0}}^{t} \mathrm{~A}(\tau) d \tau\right] \mathrm{X}_{0}$
4. none of these