After ruling the tennis world for almost five years, Roger Federer is adjusting to life at NO.2. But, like any king whose throne has been taken away, the Swiss star is already planning secretly his return to power, beginning at this week's US Open. The problem is, many experts think he will never do it. They blame everything from age and tough competition to his racket and psychology. For years Federer, 27, had enjoyed the view from the top. Competitors saw him as undefeated, and for the most part he was. However, before the 2008 season began, Federer had an illness that stole his strength and clearly affected his play on the court. Ever since, he has struggled to return to form, winning just two of his last 14 tournaments. "Twenty-seven is an age when _ ." tennis great John McEnroe told the New York Times. Pancho Sefura, another tennis great, noted that Federer is also facing a maturing crop of young talents. "There are too many great players now," he said, naming Britain's Andy Murray, 21, and Latvia's Ernests Gulbis, 20. US magazine Sports Illustrated tennis columnist Jon Wertheim suggested that part of Federer's problem could be his insistence on using a small racket. He says that the smaller head demands ball control. But we see time and again that racket makers try to get players to use a certain stick -- one they would like to market to consumers and it has a negative effect the professional game. Sports psychologist Jim Loehr told the Times that Federer is probably feeling "a sense of doubt" after being considered as undefeated for so long. If Federer is to recover his state of being undefeated, Loehr said he must overcome his doubt. "Federer doesn't need fame and money. But he has to get better. He has to go to a whole new level. That's the only way he stays in the game," he said. As for beginning his first Grand Slam in ages as the NO.2 seed, Federer said it might be for the best. "Five years almost, I was expected to win every tournament I entered," he said, "so maybe Rafael Nadal now feels what I had to feel for a very long time. It will be interesting to see how he handles it." From the passage, we know the main reason why Federer's throne was taken away is that   _  .
he is becoming older and older. he insisted on using a small racket. he is facing a maturing crop of young talents. he had an illness that stole his strength.
Question: After ruling the tennis world for almost five years, Roger Federer is adjusting to life at NO.2. But, like any king whose throne has been taken away, the Swiss star is already planning secretly his return to power, beginning at this week's US Open. The problem is, many experts think he will never do it. They blame everything from age and tough competition to his racket and psychology. For years Federer, 27, had enjoyed the view from the top. Competitors saw him as undefeated, and for the most part he was. However, before the 2008 season began, Federer had an illness that stole his strength and clearly affected his play on the court. Ever since, he has struggled to return to form, winning just two of his last 14 tournaments. "Twenty-seven is an age when _ ." tennis great John McEnroe told the New York Times. Pancho Sefura, another tennis great, noted that Federer is also facing a maturing crop of young talents. "There are too many great players now," he said, naming Britain's Andy Murray, 21, and Latvia's Ernests Gulbis, 20. US magazine Sports Illustrated tennis columnist Jon Wertheim suggested that part of Federer's problem could be his insistence on using a small racket. He says that the smaller head demands ball control. But we see time and again that racket makers try to get players to use a certain stick -- one they would like to market to consumers and it has a negative effect the professional game. Sports psychologist Jim Loehr told the Times that Federer is probably feeling "a sense of doubt" after being considered as undefeated for so long. If Federer is to recover his state of being undefeated, Loehr said he must overcome his doubt. "Federer doesn't need fame and money. But he has to get better. He has to go to a whole new level. That's the only way he stays in the game," he said. As for beginning his first Grand Slam in ages as the NO.2 seed, Federer said it might be for the best. "Five years almost, I was expected to win every tournament I entered," he said, "so maybe Rafael Nadal now feels what I had to feel for a very long time. It will be interesting to see how he handles it." From the passage, we know the main reason why Federer's throne was taken away is that   _  .
A. he is becoming older and older.
B. he insisted on using a small racket.
C. he is facing a maturing crop of young talents.
D. he had an illness that stole his strength.
Answer: