The underlined word "impair" at the end of Paragraph 2 can best be replaced by ______.

A．Most countries do not have an effective law on organ transplantation.
B．The traditional way of asking for permission of relatives for organ removal does not prove to be always feasible.
C．It is hard to understand why people should remain silent on compulsory postmortem exam after unexpected death.
D．In some countries there are laws providing that the permission of organ removal is taken for granted unless it has been refused by the person in his lifetime.

A．artificial respiration and massage of the heart have yielded no obvious result
B．a person's heartbeat and breath have totally stopped
C．standard methods of resuscitation have failed
D．the brain is certainly dead