Explanation:

- Expensive: Something that costs a lot of money. It's generally used to describe things that have a high price tag.

- Option 1, Gentle: Refers to being mild in temperament or behavior, not related to cost or price.

- Option 2, Dear: Can mean beloved or cherished, but also means costly or expensive.

- Correct answer and often used in the context of describing high prices.

- Option 3, Mild: Means gentle or not severe. Doesn't relate to cost or being expensive.

- Option 4, Sober: Means not intoxicated or serious. Again, not linked to expense or financial cost.