lesson doesn't explain ce sont vs ces sont?

Question

I got it wrong for using ces sont instead of ce sont. Kwiz pointed me to this lesson but it doesn't explain why ces is wrong.

Accepted Answer

Ce sont des tomates fraîches? -- These are fresh tomatoes?Oui, ces tomatoes-ci sont fraîches. -- Yes, these tomatoes here are fresh.
In the second sentence, ces is a demonstrative pronoun for tomatoes: these tomatoes. In the first sentence it isn't. A good indicator would be if ces is immediatelly followed by the noun it refers to or not.

Answer

For those following here later, ‘ces’ is not a demonstrative pronoun, but a demonstrative adjective. As an adjective, it needs to be linked to a noun.