I am currently writing my bachelor thesis and have to do a small literature review for it. Unfortunately, I don't know which tense I should use. Do you write ?
I am quite confused about what tense to use.
I don't think there are any general standards. It depends on your field and, potentially, your adviser's preferences. I tend to prefer the active tense (since I think that any sentence that mentions a work kind of presents said work), but pick whatever you like as long as you are consistent about it.
(My field is maths/computer science; other domains might have common standards)
Generally speaking any are acceptable. If you focus on the authors then "did show" or "have shown" feels about right. But if you take the citation to mean the paper itself, then the present tense is fine since the paper still exists and does still show...
However, advisors can be a bit picky on some such things, so it would be good to ask whether they think it makes a difference.
In a few rare circumstances, future might even work if a paper hasn't yet appeared, as in one of your own. But, as Gnosophilon says, consistency is probably a good choice.
In almost all cases people will understand you no matter how you write it. But there are exceptions, such as when some things need to be put in historical context, perhaps with older results being replace by new research. That doesn't seem to be your concern here, though.
My preference would be option 2, the simple past. There is IMO a good reason to prefer it. Quite often it is natural to say something like "Hager et al. showed [statement]. Subsequently, Smith et al. showed [stronger statement]." This (or anything else that indicates the papers were written at different past times) doesn't really work with either of the other options.
The already-given advice to ask your advisor is good general advice for academia. It doesn't always work; some advisors are less helpful than they should be. But if they will be grading your work, they can be the most reliable about how they want it to look.
Another piece of general writing advice is to look for already-published examples in your field. A lot of papers have a section that is a small literature review - how do they do it? This is nice because you can learn more than just what tense to use.
