I have (a lot of) hats,probably more than fifty.

The teacher is (wearing) a large blue coat.

We (are / have been) trying to save the planet. (Nesse caso cabe tanto "are" quanto "have been")

It (is / has been) difficult to save money. (Como o anterior)

How many clothes do you have?

(I have) never (worn) blch clothes (A palavra em negrito parece estar errada)

Why (are we) saving food?

When I go to (the beach), I like to (swim). (Essa frase pode ser respondida de outras maneiras)

Espero ter ajudado.