Some electronic equipment can ``burn out'' during operation when its internal temperature reaches a maximum value $\mathrm{T}_{\mathrm{M}}$. For greater durability of its products, the electronics industry connects temperature sensors to this equipment, which activate an internal cooling system, turning it on when the temperature of the electronic device exceeds a critical level $\mathrm{T}_{\mathrm{c}}$, and turning it off only when the temperature drops to values below $\mathrm{T}_{\mathrm{m}}$. The graph illustrates the oscillation of the internal temperature of an electronic device during the first six hours of operation, showing that its internal cooling system was activated several times. How many times did the temperature sensor activate the system, turning it on or off? (A) 2 (B) 3 (C) 4 (D) 5 (E) 9
Some electronic equipment can ``burn out'' during operation when its internal temperature reaches a maximum value $\mathrm{T}_{\mathrm{M}}$. For greater durability of its products, the electronics industry connects temperature sensors to this equipment, which activate an internal cooling system, turning it on when the temperature of the electronic device exceeds a critical level $\mathrm{T}_{\mathrm{c}}$, and turning it off only when the temperature drops to values below $\mathrm{T}_{\mathrm{m}}$. The graph illustrates the oscillation of the internal temperature of an electronic device during the first six hours of operation, showing that its internal cooling system was activated several times.
How many times did the temperature sensor activate the system, turning it on or off?
(A) 2
(B) 3
(C) 4
(D) 5
(E) 9