What planet is the same size as earth, has no moons, and has a thick atmosphere of mostly carbon dioxide?

(Assuming you mean within the solar system)
That would be Venus. Venus and Mercury are the only two known planets without moons, and Venus is not only extremely close to Earth in size but is known for its atmosphere, which is so thick heat from the Sun gets trapped in it, creating a greenhouse effect and making Venus the hottest planet in the Solar system despite being farther from the Sun than Mercury is.

Iread this book last year so take this with a grain of salt.gene jumps from the tree to compete with finny due to the fact that gene is always trying to do better than finny. he is put under the grasp of peer pressure due to finny almost forcing him to do this. ever since he first jumped finny kept pressuring him to jump since he thought gene enjoyed jumping.rather than uses this answer you should probably just reread chapters 3-4