Law of agency (follow up)

As the post I previously made is now locked to new replies (https://opentuition.com/topic/law-of-agency-3), I’ll continue here:

I’m still not fully clear. The revision notes say:

Within authority? No liability.

But may be held liable BY THE COURT if:
• enter into contract without disclosing agency status
• acting on own behalf
• trade custom

The options for the answer to the question “an agent will NOT be liable for a contract in which of the following situations?” are:

(a) fails to disclose that they are acting as an agent
(b) has had his authority terminated by the principal but the third party is not aware of that termination
(c) intends to take the benefit of the contract for himself and fails to disclose that he is acting as an agent
(d) acts on his own behalf but does identify that he is an agent

The right answer according to the mock is (d).

(a) is the first bullet point covered in the revision notes where the agent may held to be liable by the court.
(d) is the second bullet point covered in the revision notes where the agent may be held to be liable by the court (not just subsequently by the principal chasing the money from him), but this is the right answer for the situation where the agent is NOT liable by the court. So I’m confused as the revision notes says where the agent’s acting on his own behalf he may be held liable by the court.