B, because it’s from that answer it tells you what the story is about summarized
The dark cloud was like a stain of darkness over the wide-open plain.
(Is that too advanced?)
There was a red stain on the boy's shirt as he stood in the grassy plain.
(That's a bit simpler.)
The subject is defined as the "doer of an action". In this case, the answers would be C and D. So, who is only eight years old? The subject, that is, "my brother". Who is fascinated by bridges? The subject, that is, "he". He is used here only so as not to repeat "my brother" all over again, but they have the same meaning.
Here's one
<span>He fell down because he is clumsy (internal attribution). I fell down because the furniture was haphazardly arranged (external attribution).</span>