Yo / llevar / este / reloj / la semana pasada question 2 with 1 blank¿cuándo / encontrar / (tú) / ese / corbata? question 3 with 1 blankayer / nosotros / oír / este / música / en la fiesta question 4 with 1 blankjuanjo / venderle / aquel / libros / a raquel

Here we need to form the sentences:

1) yo / llevar / este / reloj / la semana pasada  

This can be completed in the "perfect preterite" of the verb "llevar"

"Yo lleve este reloj la semana pasada"

2) ¿cuándo / encontrar / (tú) / ese / corbata?

Here again, we need to use the perfect preterite in the verb "encontrar", and change the genre of the word "ese" because the word just after, "corbata", is feminine.

"¿cuándo encontraste esa corbata?

3) / nosotros  / oír / este / música / en la fiesta  

Again, here we need to use the "perfect preterite" and correct the word "este" for the same reason as before, "musica", as most words ending with an a, are feminine words.

"Nosotros oimos esta musica en la fiesta".

4) Juanjo / venderle / aquel / libros / a Raquel

Here the verb is "venderle", and we can conjugate it in the perfect preterite, we also need to correct the word "aquel", because we are talking un plural here, so the sentence is:

"Juanjo vendio aquellos libros a Raquel"

when the outside temperature is too cold, an endothermic animal can generate heat by shivering. endothermic animals must eat much more often than ectothermic animals since it takes energy to maintain a constant body temperature.