Answer:
1. Yo _____comenzé_____ un nuevo deporte. (comenzar) 
 
2. El ___confesó_______ su mentira. (confesar) 
 
3. Ustedes ____cerrarón______el trato. (cerrar) 
 
4. Los estudiantes __entendieron____ la leccción. (entender)
Step-by-step explanation:
I do not know much about the context of your assignment/question, but the verbs in parentheses must be changed into their past tense form for them to make sense.