Final answer:
Pressure is necessary to achieve high temperatures in a steam sterilizer, which ensures effective sterilization by killing heat-resistant endospores. The correct option is A.
Step-by-step explanation:
To obtain the high temperature needed in a steam sterilizer, such as an autoclave, pressure is necessary. By applying pressure, water's boiling point increases, allowing the steam to reach temperatures higher than normal boiling point, typically around 121 °C or 132 °C at 15 to 20 psi.
The high temperature achieved through increased pressure is crucial for killing heat-resistant endospores, which is the hallmark of effective sterilization.