听力原文： Taking an afternoon nap at the desk dramatically improves workers' performance,

Bosses should welcome the sight of staff slumped over their keyboards because when they wake up their performance will increase by 35 per cent and their ability to judge the right business decisions by 50 per cent, the space research agency claims.

However, they should sleep for only 45 minutes. Any longer, they risk fallings into so deep sleep and will wake up groggy.

The research was aimed originally at predicting the performance of astronauts on long missions. However, the scientists behind the study said that the same results had been achieved by office workers performing less glamorous tasks.

Mark Rosekind, chief scientist of California-based Alertness Solutions, said that many managers believed it was an admission of weakness to give in to tiredness. "It is a false myth that if you sleep more hours awake you are more productive," he said. Most people suffer a decline in their alertness between 3p..m. and 5 p. m., when they could most benefit from taking a nap. Mr. Rosekind said that napping was especially important in safety-critical jobs, such as piloting passenger jets on long-haul flights. "Controlled rest on the flight deck improves alertness in the final critical phase," he said, and maximum alertness was normally achieved between 9-11 a.m. and 9-11 p.m.

According to the research by NASA, an afternoon nap ______.

A．can greatly improve the efficiency of work

B．can fall into a deep sleep and will wake up groggy

C．makes people suffer a decline in their alertness

D．is an admission of weakness