Question

POR FAVOR AYUDA URGENTE
pasar las oraciones que están en plural a singular y las de singular a plural en ingles

Is that jacket Mario's?
Are these dictionaries Alex's?
Those are mine.
This building is not very old.
This is a good exercise
These are not the old dresses.
These are not the old dresses.

Answer 1

are those jackets mario's ?(creo que escribiste mal la oracion porque se escribe mejor is that mario's jacket?, por si te equivocaste aqui te dejo por si es la que te deje un poco más arriba. are those mario's jackets?)
is this dictionary alex's? (are these alex's dictionaries? - are this alex's dictionary?)
this is mine
those buildings are not very old
those are a good exercises
this is not a good dress
espero que te sirva!!!