1. The correct answer is las uvas.
Una ensalada de frutas is a fruit salad. Las uvas are grapes, so that would be the thing you put in a fruit salad. Las zanahorias are carrots, la cebolla is onion, and la carne is meat, so obviously those things wouldn't really belong in a fruit salad.
2. The correct answer is Quiero pollo.
This sentence literally translates as I want chicken. Prefiero pollo means I prefer chicken. Debo comer pollo means I have to eat chicken. Como pollo simply means I eat chicken. If you want to show your desire for something, you need to use the verb quierer.
3. The correct answer is el helado.
La cena is dinner, and el helado is ice cream, so you wouldn't normally eat ice cream for dinner. La carne is meat, el pollo is chicken, and el pescado is fish, all of which are commonly eaten for dinner, whereas ice cream is not really.
4. The correct answer is una bebida.
Tengo sed means I am thirsty, and una bebida is a drink. So you would offer a drink to someone who is thirsty. Una cena is dinner, un postre is dessert, and unas uvas are grapes, none of which would really help someone who is thirsty.
