Consider the following:1.Aarogya Setu2.CoWIN3.DigiLocker4.DIKSHAWhich of the above are built on top of open-source digital platforms?

1. A

   1 and 2 only

   1 and 2 only. DigiLocker and DIKSHA are also open-source stacks.

2. B

   2, 3 and 4 only

   2, 3 and 4 only. Aarogya Setu is counted too.

3. C

   1, 3 and 4 only

   1, 3 and 4 only. CoWIN is in the set.

4. D

   1, 2, 3 and 4

   All four. All four India Stack / open-source public digital platforms in this listing.

Summary. Official key is (d) all four. Aarogya Setu, CoWIN, DigiLocker and DIKSHA are built on open-source digital public infrastructure rather than closed proprietary stacks as the paper frames them.