Final answer:
In this situation, Mr. Mark, as the sole owner of the property, must sign the listing agreement.
Step-by-step explanation:
In this situation, the person who must sign the listing agreement is Mr. Mark. Since the property is owned in severalty, it means that Mr. Mark is the sole owner and has the authority to enter into the listing agreement.
The fact that Mrs. Mark had to leave for an emergency does not affect the requirement for Mr. Mark to sign the agreement as the owner of the property. As long as Mr. Mark reached an agreement for the listing price, he has the authority to sign on behalf of himself as the property owner.
It is important to note that in real estate transactions, it is usually required that all owners of the property sign the listing agreement. However, in this specific case, since Mr. Mark owns the property in severalty, he can sign the listing agreement on his own behalf.