Most discussions of the factors contributing to improvements in public health greatly underestimate the influence of the values held by individuals. This influence is indicated by the fact that the astonishing decline mortality from infectious disease during the past century was primarily due to an improvement in living conditions. To a substantial degree, these improvements depended on the emphasis by an increasing share of the population on cleanliness, prudence, and moderation.
The main point of the passage is made primarily by

A．analyzing existing data on medical practices and health outcomes.

B．presenting a set of related cause-and-effect assertions.

C．applying several general principles to a specific case.

D．presenting a general observation and supporting it with several specific examples.

E．(E) refuting in detail a commonly accepted argument.

胚胎早期红细胞在卵黄囊生成，妊娠10周起，肝是红细胞生成的主要器官，以后骨髓、脾逐渐有造血功能。