How many different linear arrangements are there of the letters A, B, C, D, E, F for which

(a) A and B are next to each other?
(b) A is before B?
(c) A is before B and B is before C?
(d) A is before B and C is before D?
(e) A and B are next to each other and C and D are also next to each other?
(f) E is not last in line?