"They are not warm."
Translation:Ele nu sunt calde.
Adjectives usually vary with the gender of what they characterize. It should be "Ei nu sunt calzi"
They are, but even things in plural have genders and so some adjectives have 4 forms: cald - caldă - calzi - calde (masc. sg. - fem. sg. - masc. pl. - fem. pl.). "Ele" is used for a group of all feminine stuff and adjectives describing it must be in their feminine plural form. "Ei" is used for groups with at least one masculine member and adjectives have to be in their masculine plural form.