Can someone review my answers and tell me if they're wrong?

question 13 - fill in the blank with the correct form of the imperfect tense.
los alumnos ( estudiaban ) para el examen.

question 14 - fill in the blank with the correct form of the imperfect tense.
los pajaros ( volaban ) sobre los arboles.

question 15 - fill in the blank with the correct comparative of mas or menos.
el hipopotamo es ( menos ) alto que la jirafa.

question 16 - fill in the blank with the correct comparative of mas or menos.
el leon es ( mas ) valiente que el burro.

question 17 - fill in the blank with the correct form of the imperfect tense.
yo ( trabajaba ) los fines de semana.

question 18 - fill in the blank with the correct comparative of mas or menos.
la gallina es ( mas ) grande que el pollito.

question 19 - fill in the blank with the correct form of the imperfect tense.
yo ( era ) muy inteligente.

question 20 - fill in the blank with the correct comparative of mas or menos.
el chivo es ( menos ) grande que la vaca.

question 21 - f ill in the blank with the correct form of the imperfect tense.
juanita ( esperabas ) el autobus.

question 22 - fill in the blank with the correct form of the imperfect tense.
tu ( ibas ) al cine.,

In Spanish (Castilian) the imperfect tense (indicative mode) is used to:  

1. talk about past habitual actions (adding used to in its different forms)

2. describe what someone was doing when it was interrupted by someone (or something) else. In fact, is more a combination of the past tense and a continuous or repeating aspect. Frequently, this includes a sense of incompletion in the verb, but not always. (Is the equivalent to the Past Progresive Tense in english)

In other words:

It is specially used to describe what used to happen or what was happening.

Knowing this, let’s begin with the answers related to the imperfect tense:

In this sentence we are talking about students, which are the third person in plural they.  

Now, the imperfect tense of the spanish verb estudiar (to study) with the third person in plural ellos (they) is estudiaban.  

Therefore the complete sentence is:

The students were studying for the exam

In this sentence we are talking about birds (pájaros or aves) which is a plural noun.

Now, the imperfect tense of the spanish verb volar (to fly) with the third person in plural ellos (they) is volaban.  

Therefore the complete sentence is:

The birds were flying over the trees

This sentence is a good example of the usage of the imperfect tense to talk about past habitual actions with the addition of used to.

Here we are talking about the first person in singular yo (I), and the imperfect tense of the spanish verb trabajar (to work) with this subject is trabajaba.  

Therefore the complete sentence is:

I used to work on weekends

In this sentence we are talking about the first person in singular yo (I). The imperfect tense of the spanish verb ser (to be) with this subject is era (was).  

Therefore the complete sentence is:

I was very intelligent

In this sentence Juanita is the third person in singular ella (she), this means the imperfect tense of the spanish verb esperar (to wait) with this subject is esperaba.  

Therefore the complete sentence is:

Juanita was waiting for the bus

This is a sentence written with the second person in singular tú (you) and the imperfect tense of the spanish verb ir (to go) with this subject is ibas.  

Therefore the complete sentence is:

You were going to the movie theater (cinema)

Now, if we are comparing the characteristics (superiority or inferiority) of two persons, animals, things or two groups; generally in Spanish we use the words más and menos, as follows:

or

The following sentences are a good example of these comparisons:

In this sentence we are comparing the stature of two animals, the hippopotamus and the giraffe, where the first one results to be less tall than the second . This means in this case we have to use the following rule:

Subject + verb (to be) + menos + alto (adjective: tall) + que…

The hippopotamus is less tall than the giraffe

In this sentence we are comparing the bravery of two animals, the lion and the donkey, where the first one results to be braver than the second. This means in this case we have to use the following rule:

Subject + verb (to be) + más + valiente (adjective: brave) + que…

The lion is braver than the donkey.

In this sentence we are comparing the size of two animals, the hen and the chicken, where the first one results to be bigger than the second. This means in this case we have to use the following rule:

Subject + verb (to be) + más + grande (adjective: big) + que…

The hen is bigger than the chick.

In this sentence we are comparing the size of two animals, the goat and the cow, where the first one results to be smaller than the second. This means in this case we have to use the following rule:

Subject + verb (to be) + menos + grande (adjective: big) + que…

The goat is less big than the cow (or The goat is smaller than the cow)

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