Learn Italian: Le fragole sono ottime, ma costano troppo. - The strawberries are excellent, but they cost too much.

The singular is la fragola (the strawberry). In Italian, most feminine nouns ending in -a change to -e in the plural, and the feminine singular "the" changes from la to le.

Why does the adjective ottime end in -e?

Ottime means "excellent" and describes le fragole. Since the strawberries are feminine and plural, the adjective must match. The base dictionary form is ottimo, and its feminine plural form is ottime.

Why doesn't troppo change to troppe to match the feminine plural strawberries?

Just like quanto in this lesson, troppo never changes when it acts as an adverb describing a verb. Here it describes how much they cost (costano), so it stays as troppo. It would only change to troppe if it were an adjective attached to a noun, like in troppe fragole (too many strawberries).

What is the base form of the verb costano?

It comes from the regular verb costare (to cost). The -ano ending tells us it is in the "they" form, which makes sense because it is the strawberries doing the costing.