Gratuitous contract  is a contract in which one party only enjoys contractual rights without paying any price. In other words, one party to the contract gives a certain benefit to the other party, and the other party does not have to pay any price to obtain the benefit.
According to the above definition, which of the following options is not part of a gratuitous contract?
A wants to go abroad to study for half a year, and is unwilling to rent out the newly renovated house, so he negotiates with his friend B to hand over his house to B to take care of it on his behalf