My approach is to use the st.1 and st.2 and see if we can allocate a 0 to January and spread out the remaining 66 successfully. if that cannot be done then obviously someone needs to have a Jan birthday.
Using st.1 - If Jan=0, Feb=6,Mar=5, and all remainder months are 6. We will need to allocate 7 to december which violates that max allowable is 6. So St.1 is sufficient
Using st.2 - Lay it out similar to above....so it is sufficient.
I would go with D.
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