What is a good defentition of theme

Which sentence contains correct capitalization? in “the rime of the ancient mariner,” the albatross was initially an omen of good luck. in “the rime of the ancient mariner,” the albatross was initially an omen of good luck.

Me read the letter. dear aunt mary, you for the wonderful painting. you are so talented! i was thrilled that you chose to paint horses. you must have remembered that i was crazy about horses when i was a little kid—and i still love them. i have hung the painting in my room so that i can see it every morning when i wake up. your loving niece, celia what makes this letter appropriate for its intended audience? it is written from the third-person point of view. it is concise and impersonal. its sentence structure is varied. its language is informal.

Dogs make wonderful pets because they us stay happy and healthy. the topic sentence is "dogs make wonderful pets." , is this correct? i keep doubting myself.