HMAC and non-repudiation

This was a question on an exam:

Two persons are using a one way communication channel and the HMAC functionality (concretely HMAC-SHA1). Choose the correct statement below:

1) We can prove who the sender is, because HMAC-SHA1 uses a shared secret, which is known to both of them. Even more, the communication channel only works in one way.

2) We can prove who the sender is, because HMAC-SHA1 uses a shared secret, which is known to both of them.

3) The sender can deny that he sent the messagge, because confidentiality wasn't provided.

4) Nothing of the above.

The questions on this exam are known to be tricky. I'm thinking answer 3 or 4 is correct ( you need a digital signature to provide non-repudiation and confidentiality has nothing to do with non-repudiation), but am leaning towards the fourth answer.

Which one would you choose?