Hi Virendra,
For your case you should do the following:
1) Create subproject (B) in your project (X). Just the subproject, with the same name. After doing this you'll have a new subproject under project (X).
2) Copy object (C) under new subproject in project (X).
Best Regards!
Mgitur
PS: in LSMW go to menu Goto->Administration to execute both steps.