In the presence of NBS, what is the least favorable product in the reaction of 1,3,3-trimethylcyclohexene?
a. 1,2-dibromo-3,3-dimethylcyclohexane
b. 1,1-dibromo-3,3-dimethylcyclohexane
c. 1,3-dibromo-2,2-dimethylcyclohexane
d. 1,4-dibromo-2,2-dimethylcyclohexane