Haber! Students quickly learn about 'hay' in present tense meaning 'there is or there are'. However, when learning about the past tenses, el pretérito y el imperfecto, students are confused on HUBO vs. HABIA.
This learning tool gives 10 examples that require students to choose either hubo or había.
This PowerPoint could be printed as a note sheet for a homework or in-class activity that could easily accompany the PowerPoint as a whole class drill.