I have a problem in Learn Basic Arabic course

My name is Lena. I’m studying a few courses at Memrise and I really enjoy them. I have a problem in Learn Basic Arabic course. In Arabic each letter has 4 variants of writing, depending on where it is placed in a word (single, initial, middle and end). When doing classic review/listening skills of the Arabic letters I hear a letter and I know which letter it is, but I’m given few variants of the letter, so how should I know which one exactly I should choose. Sometimes I guess but mostly no, and these letters go to Difficult words. And that what bugs me because I know them! Screen shots attached. Maybe it is possible to make all the variants right or only one variant of the letter among other letter should appear.