When to use "ceux / celles" for "these"

Question

What's wrong here? I use these tomatoes. These are the last ones.Ce sont is correct.Ceux-ci is marked as wrong.

Maarten Kamp · Accepted Answer

HA, 
Regardless of what might be a reasonable alternative depending on context, ‘ ceux-ci ‘ could not be correct as ‘ les tomates ‘ would need to be represented by the feminine plural demonstrative pronoun ‘ celles(-ci) ‘, if choosing this structure.
If the question was attached to the lesson you linked, the answer is not a free choice of all possible expressions though.
https://progress.lawlessfrench.com/revision/grammar/how-to-express-the-one-the-ones-celui-celle-ceux-and-celles-demonstrative-pronouns