yes Sunday and the option B is correct. For exactly FOUR Monday and Friday and the complete week 31/7=4 weeks and we have to find out otehr consecutive days (which doesnot include Monday and Friday)beyond complete FOUR weeks. Hence the will be TUESDAY,WEDNSEDAY ,THURSDAY on 29 th ,30 th,31st of January of that year.
Hence 28 th will be Monday,and so on 21 st will be Monday.Hence 20 th will be SUNDAY and the option A is correct.