GMAT Sentence Correction (SC) | Re: QOTD: Prairie dogs live in tight-knit colonies

Prairie dogs live in tight-knit colonies, called coteries,of roughly a dozen of them, that consist of several breeding females that often stay together for their entire lives, one or two breeding males that tend to switch coteries frequently, and their new pups.

(A) of roughly adozen of them, that consist of several breeding females that often stay together for their entire lives, one or two breeding males that tend to switch coteries frequently, and their new pups.

(B) of roughly a dozen