Final answer:
Inferences are conclusions or interpretations based on observations, while observations are factual statements about what can be directly observed or measured.
Step-by-step explanation:
Inferences are conclusions or interpretations based on observations, while observations are factual statements about what can be directly observed or measured. In the given examples, (a) and (b) are observations because they describe a direct observation of someone's emotion and the state of the milk. However, (c) and (d) are inferences because they involve making assumptions or interpretations based on the available information.