1) es bonita.

esto

esta

este

2) ¿cuál de estos animales es un mamífero (mammal)?

el pez

la orca

el cangrejo

3) ¿cuál de estos animales no vive en el mar?

el pez

la orca

el loro

4) en español, the “sand” es

5) fill the blank with the correct demonstrative adjective.

cangrejo es feo. (this)

6) fill the blank with the correct demonstrative adjective. (these)

me gustan bonitos.

7) fill the blank with the correct demonstrative adjective.

sons muy sucios. (those)

8) fill the blank with the correct demonstrative adjective.

pez es feo. (that)

9) fill the blank with the correct demonstrative adjective.

voy a comprar vieja. (this)

This question stands for demonstrative adjectives, such as este, ese and aquel. So these adjectives demonstrate a quality about the noun they modify. Here that quality is the location in respect to the speaker or the listener. Este is used to point out something near to the speaker in space or time. Since arena is a feminine noun, este changes to esta for matching this noun in gender. Therefore:

IN SPANISH:

Esta arena es bonita

IN ENGLISH:

This sand is beautiful

The killer whale or orca (also kwon as Orcinus orca) is a toothed whale that belongs to the oceanic dolphin family. This animal belongs to the class Mammalia. This is a type of a warm-blooded vertebrate animal of a class that is distinguished by the possession of hair or fur, the secretion of milk by females for the nourishment of the young.

El loro that translates into parrot and is a tropical bird, often brightly colored, with a short down-curved hooked bill, grasping feet, and a raucous voice, found commonly in the tropics and feeding on fruits and seeds. It is often kept as a pet and can be taught to copy what people say.

Sand translates into la arena and is a pale brown substance that you find at the beach or in the dessert, formed from very small pieces of rock. The word arena is a feminine noun, that's the reason why the definite article that  determines this noun is la (feminine and singular definite article)

Este translates into this and just as we said above, this is used to refer to something near to the speaker in space or time. Since I, the speaker who is describing a crab (saying that it is ugly), am near the crab and cangrejo is a masculine and singular noun, I need to use the demonstrative adjective este.

Estos translates into these and is masculine plural form of este. So, in this sentence fishes are also near the speaker. So I am saying I like these beautiful fishes. The reason why we choose estos is because peces is a masculine and plural noun. Therefore, demonstrative adjectives must match the noun they determine in both gender and number.

Ese indicates something more distant, that is, nouns that are further from the speaker but they can be close to the listener. In this sentence, the noun we are talking about is cerdos, which is masculine and plural. The demonstrative adjective that matches those and is masculine and plural is esos that comes from ese.

Ese translates into that and must be used here because pez is a masculine and singular noun. So here the fish is further from the speaker but it nos not necessary that it is close to the listener. So suppose you are the speaker and I am the listener, then the fish is further from you but it can be near me.

Since canasta is a feminine and singular noun, we must use the demonstrative adjective esta. So here the basket is near to the speaker in space. Since we are talking about location, then we are talking about space here. Therefore, my purpose is to buy this old basket.