Coherent waves are generated at $P$ and at $Q$ and spread outwards in every direction. The line $RS$ lies midway between $P$ and $Q$ and is at right angles to the line joining $P$ and $Q$. The distance $RS$ is much larger than the distance $PQ$. On which line, or lines, can an interference pattern be seen?
- Aboth $RS$ and $XY$
- B$RS$ only
- C$XY$ only
- Dneither $RS$ nor $XY$