Greetings once again, Gary :)
- Why is Tom Robinson unable to use his left arm? -
B) It got caught in a cotton gin.
(B) is correct because Reverend Sykes tells the children (Scout, Jem, and Dill) that Tom got his hand caught in a cotton gin when he was a child.
~Hope I helped!~
The correct answer would be conflict because this seems to be the part of the story that something bad is going to happen. I wouldn't say it would be climax, because we don't have enough information to say this is the part where everything changes. Hope this helps!