Sorry, the method of bracketing 's' made it disappear in my first post! I've fixed it now. My question again is 'Why did you put 'an' before those [ s ] sounds? What do you think the a/an rule is?'
That where I think is tricky. I know before vowels I should put 'an' instead of 'a'. And I unconsciously use "an" before vowels in speaking. I thought an (:) or a, which one?) '?' is at the beginning of these s-words, but I look up in dictionary and I've just figured out that there is no '?' at the beginning. Wow, I was pronouncing them quite wrong, not completely but I could pronounce better. How