I think, materials collided due to strong gravitational forces..
I believe it is class, because species are divided into different classes, but families, for example: there's the cat family, and there's the dog family. classes: the carnivores, herbivores, omnivores OR mammals, egg laying, or hermaphrodites
I'm assuming the answer would be greenhouse gas.
Greenhouse gases are those that trap infrared radiation (from the sun) and contribute to the greenhouse effect.
Http://groups.molbiosci.northwestern.edu/holmgren/Glossary/Definitions/Def-C/chrom_theory_inheritanc.... <span>The theory that chromosomes are linear sequences of genes. The unifying theory stating that inheritance patterns may be generally explained by assuming that genes are located in specific sites on chromosomes.
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