Preterite Conjugations - "i" -> "y" (-uir)

Question 1

In ___ verbs. Only the ____ and ____ form gets changed. The __ turns into these endings. (Pret.)

Answer 1

In -UIR verbs. Only the Él/ELLA/USTED and ELLOS/ELLAS/USTEDES form get changed.
The IR turns into these endings.

Question 2

Él/Ella/Usted Ending (Pret. -uir “i” -> “y”)

Answer 2

• yó
  example: él construyó

Question 3

Ellos/Ellas/Ustedes Ending (Pret. -uir “i” -> “y”)

Answer 3

• yeron
  example: ellos construyeron