The correct option is D When a member remains absent from the Parliament sessions for more than 60 days without permission.
The seats can fall vacant in the Parliament. This can happen in multiple ways:
1) If a member voluntarily resigns by writing a letter to the Presiding Officer of the House.
2) If a member remains absent from the Parliament sessions for more than 60 days, without permission.
3) If a member is disqualified.