Suppose in a Trust Game, Any Amount Sent by the Trustor

Suppose in a trust game, any amount sent by the trustor is multiplied by 2 (i.e. doubled) and given to the receiver. With regards to this trust game, all but one of the following options will guarantee that the trustor ends up making exactly his/her initial endowment or even less. Which is the only option where this is not true?

A) trustees return more than half of any amount received.
B) trustees return less than half of any amount received.
C) trustees return less than one-third of any amount received.
D) trustors keep their initial endowments.