3. The angle between planes $\alpha, \beta$ is $40^{\circ}$, and through a fixed point $P$ in space, the planes that form an angle of $70^{\circ}$ with both $\alpha$ and $\beta$ are ( ).
A. 1
B. 2
C. 3
D. 4
3. $\mathrm{C}$

First, draw perpendicular lines $a, b$ to $\alpha, \beta$ respectively through point $P$, then consider how many lines $l$ passing through $P$ and forming $70^{\circ}$ with both $a$ and $b$ exist.