A primary school teacher can not take it for granted that his pupils always do their homework ______.

A．Legal and ethical problems of organ transplantation.
B．Some underlying principles on organ transplantation.
C．The diagnosis of death before organ transplantation.
D．The difference between compulsory postmortem exam and organ transplantation.

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 seem feasible.
C．Many people debate on compulsory postmortem exam after unexpected death.
D．In some countries an organ removal is permitted by law if it has not been refused by the person in his lifetime.