  We prove the unique weak solvability of time-inhomogeneous stochastic
differential equations with additive noises and drifts in critical Lebsgue
space $L^q([0,T]; L^{p}(\mathbb{R}^d))$ with $d/p+2/q=1$. The weak uniqueness
is obtained by solving corresponding Kolmogorov's backward equations in some
second order Sobolev spaces, which is analytically interesting in itself.
