At which temperature does the water reach 80°C starting from 15°C?

• A. 55°C
• B. 60°C
• C. 70°C
• D. 80°C

Answer: (D)

When determining at which temperature water reaches 80°C starting from a lower temperature of 15°C, it's essential to analyze the concept of temperature progression. The water is initially at 15°C, and to reach 80°C, the temperature must increase continuously from that starting point.

Since 80°C represents the target temperature for the water, it inherently implies that once the water reaches this point, it can be considered to have "reached" the specified temperature. Therefore, 80°C is the final state we are trying to attain.

The choices given provide lower temperatures than 80°C, making them incorrect for indicating when the water attains 80°C, as the water has not yet reached that temperature at those lower values. Thus, the only correct answer is 80°C itself, as it is the definitive point at which the water reaches the desired temperature.