I'll give Brainliest :)

What is the theme/moral of this short story?

The crisp air was making colorful leaves fall around Kate while she was walking out of the large park. It had a lake and many trees that were in the middle of changing colors, and was surrounded by lots of tall, gray skyscrapers. All the normally illuminated billboards were not on, and the whole city seemed to have no power. Meanwhile, her teacher, Mr. Jacks, was walking with her. They had just gotten out of an airport hangar, where an odd forcefield had trapped them for several days. Kate had figured out how to escape, and now the people trapped along with them had gotten out and were in the city that surrounded the airport, Philadelphia. The city didn’t seem to have a forcefield around it, but something was still wrong.
Kate walked with Mr. Jacks. She was determined to figure out why the forcefields existed. Everything seemed to be empty, except one large warehouse. They walked into the warehouse, where half of the city seemed to be, looking for answers.
“Hey!” A man sitting on a sleeping bag shouted.
“Uhm, hi.” Kate stammered. “What is this place?”
A woman answered this time, “Why, this is where we’ve been living. These forcefields have cut off electricity and food. There are only a few places with power, and this is one of them”.
Kate thought about it. This was probably the safest place until they figured out how to get rid of the forcefield. Maybe she could talk to the other people to find answers. She asked Mr. Jacks, and he agreed.
“Can we stay?” She asked the woman.
“Of course! We have some sleeping bags over there.” The woman said.
Eventually, they found a comfy spot in a corner and sat down. Kate called her mom, as there was service, and she was glad to hear her parents were okay. After that, they listened to the stereo next to them. It played 80’s tunes until it started buzzing.
“Can you hear me?” A warbly voice said. “Your world is in trouble. We need to make one forcefield around your planet, instead of tiny ones. But it will come with a price.”
A man’s voice responded, “What is the price, Ayala?”
"We want more test subjects, your people. The percentage of people we take will go up.” Ayala told him.
It took a while for the man to respond, “It must happen. The other governments say it’s necessary.”
“All right.” She replied, then hung up.
A shocked silence sat in between Mr. Jacks and Kate. The government had made a deal with extra-terrestrial beings? It certainly seemed like it. But why? The sun was setting, and she was tired, so Kate decided to call it a day. After they woke up, they ate breakfast with everyone else. Soon afterwards, Kate asked Mr. Jacks if she could go exploring.
“By yourself?” He exclaimed. “That’s too dangerous.”
“Please, Mr. Jacks. I want to find out what’s going on.” She begged.
In the end, he agreed, so Kate headed out.
She saw that the power was back on and all the other forcefields you could see for miles were gone, replaced by a single large one covering the world. Out of nowhere, a hole opened in the forcefield. A small ship was coming down, made of metal and a solid red material. Kate was frozen in place. This is how people were disappearing, by ships. A light shown down on her, and everything went black.
When Kate woke up, the first thing she noticed was how weightless she felt. She must be in space. The thought was crazy, but she knew it was the truth. She was in a bedroom that looked like hers at home. A man with purple tinged skin and large black eyes led her out of the room into what looked like the center of the ship. There was her favorite food on a table.
For the next few days (or what seemed like it) she became friends with the others on the ship, and started enjoying herself.
She was talking to her friend Natasi, who looked a lot like Kate, when she thought she should ask a few questions she’d been avoiding.
“Hey Natasi? Why am I here?” She asked.
It took a while for Natasi to respond, “The truth? We are seeing if you are loyal. Many of my kind would love to have a human friend, and we are testing if it is a good idea. When we made a deal with your government for the protection against the comet, we—”
“There’s a comet coming?” Kate screeched.