Sentence 1 is the topic sentence. other sentences are based on 1 to support sentence 1, elaborating the topic sentence.
This is true. It is proper to wait for intermission to enter because entering beforehand could cause disruption and distraction from the concert which is considered very rude.
Is the brain completely resistant to injury? unfortunately not... but the skull makes it more robust, more protected... in the result: less vulnerable (answer A.!)
It's a book describing life in the woods.