According to the passage, what problem does the recent research find？A．Sleep shortage has

According to the passage, what problem does the recent research find？

A．Sleep shortage has become a worldwide problem.

B．Developed nations don"t pay enough attention to sleep.

C．Sleep problems are more serious in developing countries.

D．Lack of sleep is more obvious in developed countries.

请帮忙给出正确答案和分析，谢谢！