Correct answer: A. Long asset-or-nothing call

A cash-or-nothing call with strike $30 and payout $30 can be replicated by:

• Short European call with the same strike, plus
• Long asset-or-nothing call

Why this works

• If the stock ends at $40:

  • Cash-or-nothing call pays $30
  • Short European call pays -($40 - $30) = -$10
  • Long asset-or-nothing call pays $40
  • Net: -$10 + $40 = $30

• If the stock ends at $20:

  • Cash-or-nothing call pays $0
  • Short European call pays $0
  • Long asset-or-nothing call pays $0
  • Net: $0

So the replication is exact.