PART A: How does the description of the ivy vine in paragraph 18 contribute to
the tone of the passage?

Falling of the leaves off Ivy vine describes the hopelessness of Johnsy to live and she thinks that she will also die after the last leaf falls off.

Explanation:

Ivy vine is a symbol of the determination that Sue has in her. It is the determination to keep Johnsy alive who has lost his hope and will to live and thinks that she will die when the last leaf falls of the vine.

Bit even the last leaf falls, Johnsy is lying on her bed and is alive after which Sue tells Johnsy that she is not going to die. Now Johnsy also has the will to live and do something in her life like she wants to paint and live happily in her life.

i would think its c but i'm not sure

the answer is a because the astrophel does more and sidney goes to the astrophel more than stella.