(Solved): B) atracts untir the debris hits the Earth's atmosphere; b) Maberial reentering Earth's atmoshere a ...

B) atracts untir the debris hits the Earth's atmosphere; b) Maberial reentering Earth's atmoshere after being ejected into spoce by a violent votoanic eruption: C) Elarth passing through the orbit of an old conet: D) A A smali piece of rook fragmenting os it passes through Earth's stmosphere. 54. Which of the Fve criteris that define a 'planet' was Plute unable to fultiti...? A) it is in orbat around the Sun; B) it is able to pull itself spherical while mollen: c) it has cleared its orbit of debris: D) it is not the satelite of any other object in she solar syatem. 56. To what does the 'K-T boundary' refer,...? A) A worldwide rock deposition indicating when reptiles and sealife was killed by a huge asterold impact some 238 million years ago: B) The rock division between the Cretaceous and the Triassic periods, showing traces of Iridium, indicating the impoct of a huge asterold some 85 milion years ago causing the extinction of most dinosaurs; c) A mark in the rock reoord at the end of the Cenozolic (or cretaceous period). indicating oxtinction of $90\%$ of the fishes in the oceans; D) A sudden end of the tast ice age, some 10,000 years ago, 56. What is the main source of energy that is radiated by stars? A) Less stable nuclei fuse together to form more stable nuclei that can release excess 'binding energy', which is then radiated by the muclear fusion process; B) Chemical reactions that change fydrogen into helium 8 release energy; C) Protons that are completely dostroyed and converted into pure energy, as Predicted by Einstein, according to his formula E=MC; D) The nuclear fission of heavy elements like uranium, forming helium and other light elements. 57. Our sun is about years old, and is a(n) star. It generates energy via , consuming 600 tons of per second, leaving a ash in the core. A) 4.5 billion, average, fission, helium, carbon. B) 13.7 billion, large, fusion, hydrogen, helium C) 4.5 billion, average, fusion, hydrogen, helium. D) 4.5 billion, small, fission, helium, hydrogen. 58. What is the cause of the 11-year sunspot cycle of the Sun...? A) Sub-surface magnetic fields are twisted by the Sun's differential rotation and