The preterite tense is used if the past action had a definite beginning and definite end and is often used with phrases that give a specific time frame, eg: ...

Use the preterite tense to talk about what has already happened or actions that have been completed. The preterite tense is often used with specific time frames, eg yesterday, last week ...

For example, the tense may change between the methods section and the discussion section. The abstract is usually in the past tense due to it showing what has already been studied. Example: “This ...