Bruce decides to first reduce his tendency to smack his lips, then his tendency to spit on the road, and then finally his tendency to swear. What type of research design is he employing to measure his improvement?

a$.$ Achanging$-$criterion design

b$.$ A multiple$-$baseline$-$across$-$behaviors design

C$.$ A multiple$-$baseline$-$across$-$settings design

d$.$ A simple$-$comparison design