The systems are most responsible for providing cells with oxygen and removing the carbon dioxide. a) excretory and muscular b) digestive and excretory c) skeletal and respiratory eliminate d) circulatory and respiratory

not too sure maybe olecranon process

a chair, a bed, and a toothbrush

explanation:

in 1859, charles darwin set out his theory of evolution by natural selection as an explanation for adaptation and speciation. he defined natural selection as the "principle by which each slight variation [of a trait], if useful, is preserved".