Pantalones son muy bonitos. a. esas c. aquellas b. esa d. estos

The answer is: d. estos - estos pantalones son muy bonitos.

Let's discard the other options in order to find the correct answer.

We are given four demonstrative pronouns, three of them are feminine and just one of them is masculine, besides, the statement is showing a plural masculine (pantalones) noun with a plural adjective(bonitos).

So,

a. esas (those): This a plural feminine pronoun, it refers to feminine nouns in its plural form, used to refers to something that is not near us.

b. aquellas (those): It's also a plural feminine pronoun that refers to feminine nouns in its plural form, used to refers to something that is not near us.

c. esa (that): It's also a plural feminine pronoun, referring to feminine nouns in its singular form, referring to something that is not near us.

d. estos (these): It's a plural masculine pronoun which refers to masculine nouns in its plural form, referring to something that is near to us.

So, we are describing objects that are near us.

Estos pantalones son muy bonitos

These pants are so beatiful.

Have a nice day!