Two concentric circles with different radii share how many common tangent lines? a. 0 b. 1 c. 2 d. 3

The answer is a.0

Concentric means these circles would have the same center, thus, the smaller circle must be inside the bigger circle. Any tangent line to the smaller circle wont be a tangent line to the bigger circle, since that tangent line would intersect at the bigger circle at 2 points. Any tangent line to the big circle will not touch the small circle... so the answer would be 0.