A thermistor is an electrical component whose resistance changes with temperature. Thermistor T is part of a fire alarm system. The alarm sounds when the potential difference between X and Y reaches $4.5\,\text{V}$. What is the resistance of T at the moment the alarm is triggered?
- A$90\,\Omega$
- B$150\,\Omega$
- C$250\,\Omega$
- D$400\,\Omega$