Combien coûte ce livre ?

Thanh, 

it is an ‘ inverted question ‘, - the same structure as - ‘ combien coûte-t-il ? ‘, - question word - verb - subject. However, the article-noun ‘ ce livre ‘ is used for the subject, not a pronoun. 

For example, the context could be that the book is being identified for the first time, or is one of a few under consideration and to avoid ambiguity/confusion the specific demonstrative ‘ ce livre ‘ is used, as a pronoun would not be appropriate.

From the lesson description 

“ You use the question word at the beginning of the sentence, followed by the inverted verb and then the subject. This is a more elegant and more formal way to ask questions in French. “ 

Don’t be confused by the bold ‘ inverted verb ‘ - the inversion is the reversal from the usual ‘ subject- verb ‘ order of a statement to the inverted  ‘ verb - subject ‘ structure of a question. 

The other difference is that a trait d’union is used between the verb and a subject pronoun ( plus or minus a euphonic ‘ t ‘ as needed, as in this example ), but not between verb and subject nouns. 

 Inverted questions in the present tense (Le Présent) in French - il/elle/on forms

 Inverted questions in the present tense (Le Présent) in French - regular forms (except il/elle/on forms)

Perhaps a similar inverted example with a noun could be added in relevant section of the lesson to clarify. 

Thank you Maaten K . Your explaination is very clear and easy to understand . So if i want to say "Your mother speaks France ?" with inverted question i can just write "Parle sa mère le francais ?"

Thank you cecile , i just have a wonder 

In formal case with inversion we can write "Combien coûte ce livre ?" but can we write "Parle ta mère le francais ?"  ? If not , then why ? i think "ce livre" and "ta mère" are the same , they not subject pronouns , i think they both are subject nouns. Please help me , I'm very much appreciate !