Directions for questions 78-81: Six scientists A, B, C, D, E and F are to present at paper each at a

one-day conference. Three of them will present their papers in the morning session before the lunch

break whereas the other three will be presented in the afternoon session. The lectures have to be

scheduled in such a way that they comply with the following restrictions:
B should present his paper immediately before C's presentation; their presentations cannot be separated by the lunch break. D must be either the first or the last scientist to present his paper.

In case C is the fifth scientist to present his paper, B must be