3. As shown in the figure, the base of the quadrilateral pyramid $P-ABCD$ is a square, $PD \perp$ base $ABCD, PD=AD=1$, let the distance from point $C$ to plane $PAB$ be $d_{1}$, and the distance from point $B$ to plane $PAC$ be $d_{2}$, then the size relationship of $1, d_{1}$, $d_{2}$ is $\qquad$ .
3. $d_{2}<d_{1}<1$ Detailed explanation: Using volume transformation, we can find $d_{1}=\frac{\sqrt{2}}{2}, d_{2}=\frac{\sqrt{3}}{3}$, thus $d_{2}<d_{1}<1$.