For valid attestation of an instrument under the Transfer of Property Act, 1882, it is necessary that

Under the Transfer of Property Act, 1882, for valid attestation of an instrument, all of the conditions mentioned in Options A, B, and C must be fulfilled:

Option A: "Each attesting witness must see the executant sign the instrument or affix his mark" - This ensures that the witnesses observe the act of signing or marking by the executant.
Option B: "The executant must see the attesting witness signing the instrument" - This ensures that the executant confirms the presence and signing of the witnesses.
Option C: "Each attesting witness must sign the instrument in the presence of the executant" - This ensures that the witnesses sign in the presence of the executant.

Therefore, for valid attestation of an instrument under the Transfer of Property Act, 1882, all of these conditions must be satisfied, making the correct answer Option D: All of the above.