1. A predicative nominative is a noun or a pronoun which follows a linking verb and refers to something before that verb. In your case, the correct answer is B, because "a shelter" goes after the linking verb "is", and refers to "a lean-to". 2. A participle has the form of infinitive + ing. In this case, the answer is D, flourishing.
though I can't be sure without seeing the passage first, I presume its option C) "she has a right", because it has the most assertive and passionate tone as far as I can tell.
