1. When I was choosing the Intended Field of Study, I noticed that there are three programs - "Statistics MS", " Statistics MS-Data Science" and "Statistics MS - Biostatistics", is there any difference between the "Statistics MS Program" and the other two? Or it contains the other two? All three are different options. However, the data science option is very specific and probably won't apply to you (see information athttp://www.stat.wisc.edu/ms-degree-data-science-option-ms-ds). So really, you are probably going to be choosing between the regular Stats MS and the Stats MS with Biostat option.
2. Besides, there is a question "Are you applying to the Biostatistics option?" in the supplemental application. Does the "Yes" here means I am applying for a Biostatistics Program? Yes. You should also choose the Biostat option in the main part of the graduate school application too, if your intent is to apply to the Biostat option. If you choose Stat MS with no option, it is assumed that you're applying to the regular Stat MS.