"Buy two kilograms of tomatoes."
Translation:Купи два килограмма помидоров.
My answer was "купи два килограмма помидор"... but I am not 100% sure that it is a grammatically correct option... many people would say so though.
I guess it should be помидоров, since it's genitive plural, but I might be wrong
Yes, you have to use Genitive plural there, because the English construction "X of Y" is usually replaced by Y being in Genitive in Russian.
The course is not meant for native speakers of Russian. If you speak Russian IRL you should double check your language is standard and you do not use a questionable word order.
Good point about the native Russian speakers ;) I was merely checking, because I am about to recommend this course to a few of my friends... and because I thought that the comments may be necessary for the course to graduate from beta-version.
Seriously - great job, guys!!!