It would help to have the romanisation in the correction, and even more: the IPA. This lesson would be easier for us.
You cannot put ㅅ at the end of a syllable because it soulds like ㅌ, so 아잇그림 would be aitkeurim, not aiskeurim
The sound made by ㅅ in 잇 isnt the same as 스. When it closes a syllable, it is a bit sharper, much less like the sound an s makes.
I think it's because if you used 잇 or 있 , in the korean pronunciation you wouldn't get an 's' sound. So they use 스 instead
Could you give the romanization for the characters you mentioned? The 人 and 人人 at the bottom,what is the difference in sound or use. (Sorry, I don't have a Hangul keyboard.)
잇 - it; 있 - it, 스 - seu or sŭ (latter one in other romanization). ㅅ and ㅆ are generally pronounced the same, though ㅆ is kinda louder and stronger. However both are pronounced as 't' at the end of the syllabe (this is why 잇 is 'it' when romanized)