1. When we are speaking, sometimes we use "then", sometimes "so" and although the dictionary shows the differences, it's difficult to understand them. Is there another way? (especially to explain it to students)
2. I still insist on asking you about uncountable nouns. When I don't know if the word is C or U, can I use a structure that is not incorrect? I mean, something less complicated? For example, I saw that the word "doubt" can be C or U but the examples weren't good enough. Is it right to say: "Teacher, I have a doubt"? or when they say "I like pasta", "I like potatoes". Can I accept a countable noun in the singular form (like in spoken English???). I still saw the word "activity" is uncountable in some cases, but I have an English book which says:"Extra Activities", for extra exercises. You see??? I get tired of trying to understand them.
1- Context might help. I hadn't noticed this problem before.
2- C nouns can be used in the singular. The problem with 'activity' is that some nouns can be both C & U according to context. If you are thinking about work, then it's uncountable, but if you are thinking about a tesk, or piece of work, then it is countable. Rather than labelling a noun as one or the other, think of U & C as characteristics they have, which can be different according to context:
I like coffee (substance/ drink U)
I'd like a coffee (unit of drink- C)