Which sentence from "Black Hole Beginnings" contains a cause-and-effect relationship?

More matter mounts up on the outside, increasing the pressure on the inside.
Instead it is a dramatic melding, or blending, of atoms, called nuclear fusion.
Each atom has its own tiny center, or nucleus.
Surrounding each nucleus is an electrical force field.

Which number is main idea? i need answer quick. (1) people may think that love and romantic feelings are enough of a basis for choosing a spouse. (2) the chances of a marriage surviving, however, would improve if prospective marriage partners considered a few unromantic questions before deciding on matrimony. (3) for example, do the two individuals involved share a common socioeconomic background? (4) the more similar they are in their social, economic, religious, and cultural backgrounds, the more similar their expectations about married life will be. (5) in addition, what are their goals? (6) it’s a big advantage to the marriage if they know and share one another’s goals concerning career, lifestyle, and family. (7) finally, and maybe most important, how does the prospective spouse treat others in his or her life? (8) during the courtship, the boyfriend or girlfriend may get special consideration, but in the long run, spouses will probably treat each other about the same way they treat their own family members.

Why do you think electric energy for households is generally supplied by power plants instead of by an electric generator at home.

Snakes, dogs, and humans have a vertebral column. snakes and dogs have tails, and humans have vestigial tailbones. dogs and humans have limbs, but snakes do not. most reptiles lay eggs, but a few give birth to live young. what do these structures suggest about the evolutionary pattern between the three organisms? 1. snakes and dogs are more closely related than snakes and humans. 2. snakes and humans are more closely related than humans and dogs. 3. dogs and humans are more closely related than snakes and humans. 4. dogs, snakes, and humans share a common ancestor. 5. the early ancestor of snakes and dogs is the same, and the early ancestor of humans is different.