The equation of a line passing through the point ` vec a` parallel to the plane ` vec rdot vec n=q` and perpendicular to the line ` vec r= vec b+t vec c` is a. ` vec r= vec a+lambda( vec nxx vec c)` b. `( vec r- vec a)xx( vec nxx vec c)` c. ` vec r= vec b+lambda( vec nxx vec c)` d. none of these