This question tests recall of a specific industry ranking from a Dun and Bradstreet report on India's BPO sector around 2006 to 2007, so it helps to think about each company's background and scale.
The distinguishing detail here is Genpact's origin story: because it started life as GE's captive back-office unit before spinning out, it had years of head start in scaling up its India operations before this survey was conducted, which explains why it topped the list.
Let's summarize:
So according to Dun and Bradstreet, the largest employer was Genpact, option (A).