Authentication and integrity
Q1 asks “Show how an attacker can act in place of Alice and send a file to Bob tricking him into believing that the file is coming from Alice.”

In your answer, Trudy simply relays the traffic to the two parties without doing anything else, thus this is not really an attack that achieves what is asked. Note that whatever Bob receives is truly coming from Alice in this session.

Hint for Q2: the problem in the protocol is that Bob cannot verify that the last message is fresh, and it can come from a previous session intercepted by Trudy (replay attack).