Which three styles of sake are mostly served chilled but sometimes warm?

The correct identification of the styles of sake that are mostly served chilled but can occasionally be enjoyed warm is rooted in the characteristics of these sake types. Ginjō is a premium sake that undergoes careful brewing with high-quality rice and is often appreciated for its aromatic and fruity flavors, making it ideal for chilling to highlight these attributes. Koshu, aged sake, can exhibit complex flavors and aromas that sometimes benefit from gentle warming, allowing certain taste profiles to emerge. Nigori, the cloudy sake due to coarse filtration, often has a sweet and rich profile that is typically enjoyed cold, but it can also be enjoyed warm depending on personal preference and occasion.

The reasoning behind the popularity of serving these styles chilled, with the option of warming, underscores the versatile nature of sake and its capacity to be enjoyed at different temperatures, enhancing various flavors and aromas. The other combinations listed do not align as clearly with the characteristics and typical serving practices of these sake styles, which is why they are not the correct answer.