What is the main idea of the news item？A．The mechanical breakdowns of artificial heart.B．T

What is the main idea of the news item？

A．The mechanical breakdowns of artificial heart.

B．The first artificial heart implanted in a human chest.

C．Various types of artificial pumps have come into play.

D．Doctors achieve milestone using artificial heart with no beat.

请帮忙给出正确答案和分析，谢谢！