In this talk, we will introduce Zvonkin transformations and use this methodology to solve the SDEs with singular drift b. We will show that if $|b|^2$ belongs to the Kato class $K_{d,a}$ for some $a \in (0,2)$ ($a$ can be arbitrarily close to $2$), then there exist unique strong solutions to the SDEs. Furthermore, we allow the drift to be time-dependent. In order to apply Zvonkin transformations, we need to have a better understanding for the parabolic equations with Kato class coefficients. Some new regularity estimates on Kato class and Hardy-Littlewood maximal operators will play crucial roles.