French language Q&A Forum

Another problem I have here is with the explanations in the lesson. It says that when talking about SOMETHING SPECIFIC, you should use elle/il. But then there's this example: Qui est Sylvie ? - C'est ma sœur. 

I would think that here we are talking about a very specific Sylvie, and not just some Sylvie. Then why do we say c'est instead of elle? 

In the Weekend Challenge: 'My plan for the day of the exam' one of the translations required is 'that I'll have chosen the day before'. 

The answes given are: 

'que j'aurai choisiS la veille'  OR 'que j'aurai sélectionnéS la veille'

There is no object pronoun in either of these answers, so why are the past participles 'choisi' and 'sélectionné' writen with an S added for agreement?

Thank you

Sorry, the previous one jumped out without me knowing...

As I can understand, lui/leur is more when we are addressing an action towards someone, right? je lui parle, je leur demande, etc. in the test the question was about "voler" FROM sbody. So is it an exceptional case, or is it both "to" and "from" direction? Thanks!