Directions: The following question consist of a set of four statements. One or more of the statements may have an error of grammar or syntax. Select the statement(s) having the error.

A. Sociability is as much a law of nature as mutual struggle. B. Of course it would be extremely difficult to estimate, however roughly, the relative numerical importance of both these series of facts. C. But if we ask: "Who are the fittest: those who are continually at war with each other, or those who support one another?"‌ we at once see that those animals which acquire habits of mutual aid are undoubtedly the fittest. D. They have more chances to survive, and they attain, in their respective classes, the highest development of intelligence and bodily organization.