Select the correct text in the passage. which selections in this passage are prepositional phrases? the origin of species by charles darwin (excerpt) in regard to the sterility of hybrids in successive generations; though gartner was enabled to rear some hybrids, carefully guarding them from a cross with either pure parent, for six or seven, and in one case for ten generations, yet he asserts positively that their fertility never increased, but generally greatly decreased. i do not doubt that this is usually the case, and that the fertility often suddenly decreases in the first few generations. nevertheless i believe that in all these experiments the fertility has been diminished by an independent cause, namely, from close interbreeding. i have collected so large a body of facts, showing that close interbreeding lessens fertility, and, on the other hand, that an occasional cross with a distinct individual or variety increases fertility, that i cannot doubt the correctness of this almost universal belief amongst breeders. hybrids are seldom raised by experimentalists in great numbers; and as the parent-species, or other allied hybrids, generally grow in the same garden, the visits of insects must be carefully prevented during the flowering season: hence hybrids will generally be fertilised during each generation by their own individual pollen; and i am convinced that this would be injurious to their fertility, already lessened by their hybrid origin.
