Answer:
1. es dudoso que nuestros amigos hayan llegado.
2. niego que los muchachos hayan dicho la verdad.
3. los estudiantes temen que la profesora haya calificado los exámenes.
Explanation:
Identifying the narrator and the time that a sentence indicates is the first step that must be taken. this is very important to be able to conjugate the verbs, and that these have concordance with what is being expressed