A gas contains two types of suspended particles having average sizes of $2\: \mu m$ and $50\: \mu m$. Amongst the options given below, the most suitable pollution control strategy for removal of these particles is

1. settling chamber followed by bag filter
2. electrostatic precipitator followed by venturi scrubber
3. electrostatic precipitator followed by cyclonic separator
4. bag filter followed by electrostatic precipitator