Options given:

1, 2, 3, 4 only.

Which one must be true?

Let's examine more carefully:

Case 2 (A = 2) may violate session split because F and E (5,6) are afternoon → B C must also be in same session (morning or afternoon). That restricts:

Morning session = 1,2,3

Afternoon session = 4,5,6

B and C cannot be separated by lunch break → must be both in morning or both in afternoon.

Try pairs:

Case 1: B=2, C=3 → both in morning ✔

Case 2: B=3, C=4 → across lunch break ❌ (Invalid)

Thus only Case 1 is valid.

So A = 4 MUST be true.