The greatest common factor of $10$, $28$ and $30$ is $2$. 
There are three ropes. One of them is $10$ inches long, the other two are $28$ and $30$ inches respectively. If we cut those ropes into small pieces with nothing left and each piece has the same length, how long is each piece at most? 
Options:
A. $$2$$ 
B. $$5$$ 
C. $$7$$ 
D. $$10$$ 