Answer: These are the right answers:
1. es
2. es
3. son
4. es
5. está (make sure you add the accent at the end. Otherwise it translates as "this").
6. está
7. está
8. está
9. estás
10. es
11. eres
12. estar
Explanation: Just to elaborate a little on the answer, it can also be added that in this exercise they are asking you to fill out the blank with the appropriate form of the verbs SER and ESTAR, which translate in English as TO BE. Non-Spanish speakers often find that these two verbs are difficult to differentiate. Although we would need an entire session to explain the different uses of these verbs, I would argue that generally speaking, we use ESTAR when we think that the quality is the result of a transformation, which can be real or supposed. In addition, we use it to place the subject. So, for instance, in sentence 5 it is said: "He is overwhelmed (he has become that way) with his studies (as a result of his studies)," hence the use of the verb ESTAR. We use SER in order to make general judgements, as well as to identify the subject. So, for instance, in sentence 11 it is said: "Julia, you are a good girl."