The correct option is A The book being short, I read it in two hours
Here, we have to combine the sentences by using nominative absolute construction.
A nominative absolute is a noun phrase. Most nominative absolutes contains a participle that modifies the noun and pronoun.
Option A is incorrect as subordinating conjunction 'because' is used to combine the sentence instead of nominative absolute construction.
Option B is correct as 'being' is used to combine the sentences if there is an adjective (short) after be-verb (was).
Option C is incorrect as 'so' is used to combine the sentences instead of nominative absolute construction.
Option D is incorrect as it changes the meaning of the question.