Which Has Not Been Proposed as a Likely Reason for the Relatively

Which has not been proposed as a likely reason for the relatively high infant mortality rates in the United States?

A) Changes in access to health care, clean water, and nutrition over the twentieth century
B) Country-level differences in definitions of what constitutes a live birth
C) Disproportionate conditions of poverty in certain ethnic and racial groups in the United States
D) All of the above
E) B and C