It can be - people seem to use both.
This sentence has in fact been deleted from the course database as it has an error in it, but we are still waiting for the Duolingo system to get rid of it. The correct version would be:
- Oes clust dost gyda ti - because clust is feminine and so tost must mutate to dost
how long does it take for things to be removed, it seems so many things are waiting for the system to remove it
It seems to be a system-wide problem in Duolingo at the moment which is affecting a number of courses which are in development. As a course team we do not know how long it will take to get fixed.