This is a desk and . . . . . . . . tables.

In the given statement desk and tables are being pointed out. As we can see, the answer must point out 'tables'. Thus, the answer must be a demonstrative pronoun followed by the correct form of the verb 'be' that can point out a plural object.
Option A is correct. 'Those' is a demonstrative pronoun used for plural objects and 'are' is also the form of the verb 'be' used for plural objects. 'Those are tables' is a correct phrase as 'those are' perfectly points at 'tables'.
Option B is incorrect. 'These' is a demonstrative pronoun used for plural objects, however, it is not followed by a verb. Thus, option B does not point out 'tables'.
Option C is incorrect. 'Are' is the correct form of 'be' for pointing at plural objects but, 'that' is not a demonstrative pronoun that can be used for plural objects.
Option D is incorrect. 'That' and 'is' both cannot be used for plural objects and so option D cannot be used to point at 'tables'.