If you must choose only one answer, then choose
... C. line q
Because of the way the figure is drawn, it is not clear that any of the listed items is in plane B.
For example, if line c is supposed to represent the intersection of plane B with plane M, we expect parts of plane B's edge to be dashed, indicating they are below or behind plane M. Because none of plane B's edges are dashed, we must conclude it lies entirely above and in front of plane M.