Final answer:
People typically start to feel pain due to heat at temperatures above 45°C, which can cause tissue damage.
Step-by-step explanation:
The temperature at which people begin to feel pain due to heat is above 45°C. This threshold is when heat starts to cause damage to skin and tissue, leading to a sensation of pain. It should be noted that individual tolerance to temperature can vary, but a general consensus agrees that exposure to temperatures above 45°C can result in pain and potential tissue damage. Therefore, the correct answer is (b) Above 45°C.