Joint sitting of Lok Sabha and Rajya Sabha can take place to resolve deadlock over

1. A

   Ordinary Legislation

   Article 108 allows a joint sitting of both Houses to break a deadlock on an ordinary bill. That is the official key.

2. B

   Money Bill

   A Money Bill cannot be delayed by Rajya Sabha beyond 14 days; there is no joint sitting (Article 109).

3. C

   Constitutional Amendment Bill

   A Constitution Amendment Bill under Article 368 must be passed by each House separately; joint sitting is barred.

4. D

   Appropriation Bill

   An Appropriation Bill is a Money Bill in substance; deadlock is not resolved by Article 108.

Summary. Official key is (a) ordinary legislation. Joint sittings have been rare (Dowry Prohibition, Banking Service Commission, POTA). Money, appropriation and 368 bills are outside Article 108. Honour the stored letter (a).