- Roberto lanzó la pelota.
- Tú liberaste los peces.
- El avión partió para España.
- Yo moví los muebles de mi habitación.

Normally, when in a statement he writes that the verbs conjugate with "pretérito" (past tense) he refers to the "pretérito perfecto simple" (simple past tense).
It is a simple exercise, the sentences follow a basic structure which is: Subject + Verb + Object (S + V + O).
Most of the objects (O) that sentences have are direct objects.
It should be noted that the verb must agree in number with the subject it accompanies.