What are the subjects in this compound sentence?

My brother is only eight years old, and he is fascinated by bridges.

Choose all answers that are correct.

a. years

b. bridges

c. brother

d. he

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.