The passage says "after long hesitation", which means he did not want to sell the goat, but if he did sell it, like it says he did, he must have had a good reason such as being able to support his family. This would make the answer most likely to be...
c) Reuven doesn't want to sell Zlateh, but his family needs the money. Reuven's decision and sacrifice set the plot of the story in motion. Without this event, the rest of the story wouldn't have happened.