Which excerpt from "Creepy, Crawly Healers" uses a problem-and-solution structure?

"Scientists performed a study in 1989 and discovered that maggots were safe and
useful."

"Since scientists know that spider silk has
benefits, it is being developed in a lab."

"In the late twentieth century, maggots were used only when modern practices
failed to heal a wound."

"A company in Britain has created a leech farm. It supplies leeches to doctors all over the world.”

Letter to a friend describing my boarding school.

Explanation:

ABC Avenue

12 May 2018

Dear Jack,

How are you? I hope everything is fine.

I am actually writing to you about your recent letter asking me about my boarding school.

My boarding school is located at the extreme end of the city's premises The campus is huge with a large, sprawling forest around it. But despite the huge premise, life here is boring. We are allowed to go out into town only twice a month, and that too, only for a couple of hours.

The building is majestic, with huge halls and chapels. The sleeping quarters are old and appear scary at night. We are allowed to be up till 10 and it’s lights out. The place is reminiscent of old-school buildings, with all the huge and ancient sculptures. But the ambiance is good for the students.

Please come visit soon.

Your friend

Joe.