The factors of $$30$$ are $$1$$, $$30$$, $$2$$, $$15$$, $$3$$, $$10$$, $$5$$, $$6$$, so the greatest odd factor of $$30$$ is $$15$$. 
The greatest odd factor of $$30$$ is ． 

- $$5$$ 
- $$6$$ 
- $$15$$ 
- $$21$$ 