The correct option is A Monday
B is on Tuesday. Let's take a look at Saturday, F can't be organised because it must be followed by C, D can't be organised because it must be organised before the "no lecture" day,.Since Friday is not "no lecture" day, this means D can't be organised on Thursday. Thus, E can't be organised on Saturday because there won't be any spot for D to have two days gap. Thus, only possible event on Saturday is A.
The only way to keep a gap of 2 days between E and D, having C immediately after F and D before the "no lecture" day is
D on Sunday, no lecture on Monday, B on Tuesday, E on Wednesday (2 days gap), F on Thursday, C immediately after on Friday and A on Saturday.