Sally Agrees to Mow Paul's Yard for $300 for the Summer

Sally agrees to mow Paul's yard for $300 for the summer. Paul wishes to assign the contract to his grandmother. Sally objects because Paul's yard is very small while the grandmother's yard is over an acre. Which of the following is the correct legal outcome for the dispute between Sally and Paul?

A) Sally will win because Paul's attempted assignment would increase the duties to which she agreed.
B) Sally will win because all assignments are invalid without the obligor's consent.
C) Sally will win unless Paul paid her the $300 in advance in which case Paul will win.
D) Paul will win because he may validly assign the contract without Sally's consent.
E) Paul will win so long as he tells Sally about the assignment prior to the time she begins any performance whatsoever.