Anaandika should also be accepted.
The negative you're thinking of would be
i, meaning "
you don't write." That -a on the end makes it clear that we're not dealing with the present negative.
The only possible interpretation of huandika is of the habitual form with the invariable prefix hu-. The subject in this case seems to be left up to "context" ... but seeing as there is ABSOLUTELY NO CONTEXT AT ALL in a random sentence fragment like this, it should accept all of these:
The last two are a less commonly used present tense that used to be used a lot but now only really appears in news headlines or plot synopses (or things like that where the simple fact of an action without reference to time is given). The course doesn't teach it at all, which I think is a mistake!