The BS requirement for both probability and statistics can be satisfied a number of ways. For students planning to take Machine Learning or other reasoning courses, it is strongly recommended that you take 553.420 Intro Probability and 553.430 Intro Statistics (or the honors versions).
Otherwise, any combined prob/stat course may be used, but 553.310 Prob/Stat for Physical Sciences & Engineering or 553.311 Prob/Stat for Biological Sciences & Engineering are strongly recommended.
Lastly, 553.211 Prob/Stat for Life Sciences counts toward the requirement, but is not necessarily included in the pre-req lists of all CS courses.