单项选择题

Human babies are born in immature, helpless states, owing to ______.

A．the early birth of human fetuses
B．the big brains of the fetus
C．the constricted birth canals of the mother
D．both big brains and constricted birth canals

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单项选择题

This evolution of human brains was not without its difficulties for mothers, because ______.

A．human brains started to grow larger
B．our ancestors walked upright on two legs
C．it altered our ancestors' skeletons
D．it makes the passage of big-brained infants difficult

单项选择题

What is the main idea of the passage

A．How to prescribe drags to patients who are terminally ill
B．A legal skirmishing between the Oregon law and the Supreme Court
C．A controversy over the Death with Dignity Act in Portland, Oregon
D．A debate over physician-assisted suicide in the U. S. A.