1. el lunes pasado yo (tener) una discusión con un compañero de clase.
2. la discusión (comenzar) mientras el profesor (dar) una clase sobre deportes.
3. mi compañero siempre (descutir) durante la clase.
4. el profesor no (querer) discusiones durante su clase.
5. de modo que nos (decir) : "¡silencio! ".

1. tuve

2. comenzó;  estaba dando

3. discute

4. quiere

5. dijo

Explanation:

The exercise aims for you to use conjugations in past and in present to make comparisons of time.

The present simple is used to talk about routines or current situations. In this exercise someone is telling a story that is why the conjugations are in the  indefinite past and the sentences that refer to recurrent situations in class are in the Simple Present. Also is the use of the verb ESTAR + GERUND to give the idea of an ongoing action in the past.

Here is the translation of the sentences:

1. Last Monday I had an argument with a classmate.

2. The discussion began while the teacher was teaching sports.

3. My partner always discusses during class.

4. The teacher does not want discussions during his class.

5. So he told us: "Silence!"

this question is given using the conditional form. conditional tenses are is used when talking about hypothetical situations and probabilities. also, this is used when making polite requests. so comprarías is the conjugation of the verb comprar that matches the second person singular in the conditional. finally:

¿cuál comprarías tú?

show the underlined word, so i can you. or spell it