Definition: In this task, you're given an article and an answer. Your task is to generate the question for the answer based on the given article.
Input: Article: (CNN)---NBA star Yao Ming announced his retirement during a news conference in China on Wednesday."I need to make a personal decision," Yao said."I am ending my basketball career. I am very grateful. I would like to thank my family members and my parents. And most of all, the Houston Rockets." Voted an All--Star player eight times while playing for the Houston Rockets, he was one of the most successful overseas players in the league. Yao has chalked up a career average of 19 points, 9.2 rebounds and 1.9 blocks . His field-goal percentage was 52.4. In recent years, however, he struggled with foot and ankle injuries, and missed the 2009-2010 seasons. He suffered a fracture on his left ankle, and missed last season after playing only five games. Yao has been undergoing treatment and training in recent months, but some doubted he could make a comeback. The 30-year-old said he struggled to learn English when he first came to the United States, and grew a lot during his time in the country. " 9 years ago, I came to Huston as a tall, skinny player. I grew to a man there. I also had my daughter there. I thank you all," Yao said during the packed news conference in Shanghai. Yao's retirement came the year as another NBA giant Shaquille O'Neal. Both seven-footers had battled for many years. Kobe Bryant said Yao opened up doors for Chinese players to feel they could play in the NBA."All that started with Yao," Bryant said.
Answer: Because he was seriously injured in his left ankle.
Output:
Why did Yao miss the 2009-2010 season?