Which of the following statements is correct ?

S1 : The normal temperature of the human body is 37 °C.

S2 : Heat flows from a body at a higher temperature to a body at lower temperature.

The correct option is Both S1 and S2 are inferences.

Let us understand the scientific difference between an observation and an inference:
1. Observation: An observation is direct data or information gathered using our senses or measuring instruments (e.g., measuring a specific person's body temperature with a thermometer right now and recording 37 °C).
2. Inference: An inference is a conclusion, generalization, or logical deduction drawn from a collection of multiple observations and scientific reasoning.

Now, let us analyze the two given statements:
• Statement S1 ("The normal temperature of the human body is 37 °C"): This is a generalized conclusion derived after measuring the body temperatures of a large sample of healthy individuals over time and calculating their average. Since it is a generalized scientific conclusion rather than a single direct measurement, statement S1 is an inference.
• Statement S2 ("Heat flows from a body at a higher temperature to a body at lower temperature"): This is a fundamental principle of thermodynamics concluded after analyzing numerous experimental observations of thermal energy transfer. Because it is a general scientific rule deduced from repeated findings, statement S2 is also an inference.

Therefore, both statements S1 and S2 are inferences.