Опрос от журнала "8 часов": "Чем Вы питаетесь на работе?"

Guard Patrol
The organizers of a week-long fair have hired exactly five security guards to
patrol the fairgrounds at night for the duration of the event. Exactly two
guards are assigned to patrol the grounds every night, with no guard assigned
consecutive nights. If the fair begins on a Monday, how many different pairs of
guards will be available to patrol the fairgrounds on the following Saturday
night?
A) 9
B) 7
C) 5
D) 3
E) 2