sub-contractor

client "P" entrusts a  commercial construction project to a contractor, "A".

the contractor "A" outsource a part of the project to another person "B" (a sub-contractor)

The sub-contractor further gives part of his work to yet another sub-contractor "C".

Now, questions are as follows, 

Whether "C" and also "B" are required to discharge service tax on their part of taxable service? 

If so,

whether B and A can avail CENVAT facility of service tax paid by C and B respectively