Solve 5. Answer: lines lying in two planes tangent to a cylinder of radius $d$ with axis $A B$ and passing through point $M$, except for the line parallel to $A B$ (if point $M$ is located at a distance $d$ from line $A B$, then there will be only one tangent plane and there is no need to exclude the line). Lines at a distance $d$ from line $A B$ are precisely the lines tangent to the specified cylinder. If we select from these lines those that pass through point $M$, we obtain the set described in the answer.

## Second Round

## 7 - 8 grades