Unable to understand what kind of design pattern this is?

I am not able to understand the below design. Let's assume the below classes and interfaces

interface A
{
   ....
}
class B implements A
{
   ....
}
class C extends B implements A
{
   ...
}

I found this design in one of the IBM frameworks (wcs order framework). So here why class C needs to implement A ?

What are the different scenarios in which you can use this design?

What type of design pattern is this?