Coherent waves originate at $P$ and at $Q$ and spread out in every direction. The line $RS$ lies halfway between $P$ and $Q$ and is perpendicular to the line joining $P$ and $Q$. The distance $RS$ is much greater than the distance $PQ$. Along which line, or lines, is an interference pattern seen?
- Aboth RS and XY
- BRS only
- CXY only
- Dneither RS nor XY