A pair of twin-brother ligers, a rare lion-tiger hybrid(杂种), have become superstars in China's southernmost island province of Hainan after becoming the first ligers in the country to reach their first birthday. Tens of thousands of tourists visited the liger brothers at Hainan Tropical Wildlife Park during the week-long May Day holiday that ended on Sunday, hoping to catch a glimpse of the rare animals. At least 10,000 people signed a red banner when the park celebrated the liger's birthday on May 2. People expressed the hope that the twins would be strong and healthy, the Hainan Daily reports. Zookeepers even made the twins a special birthday cake out of beef and eggs. The ligers, born on May 2, 2005 , are named 'Ping Ping' and 'An An', which together translate as 'safe and sound'. Their mother Huan Huan is a six-year-old tigress and their father is a four-year – old lion named Xiao Erhei.  The couple first gave birth to a liger in June 2004 but the cub (幼兽)  died of respiratory(呼吸的）failure 72 hours later. The pregnancy (怀孕) rate for lion-tiger couples is only between one and two percent and the cubs normally have a short life expectancy due to the differences in their chromosomes(染色体). Zoologists say only six to eight ligers are living in the world. China's first tiger-lion hybrid cub was born at Hongshan Zoo in Nanjing, capital of east China's Jiangsu Province, in 2002. But it died a week later. Ping Ping and An An have broken the survival record set by a liger who lived for 113 days at Hongshan Zoo. 1. Why can Ping Ping and An An become superstars? A. Because they are the most beautiful ligers. B. Because they are the cleverest ligers. C. Because they are the most attractive ligers. D. Because they are the first ligers to live for a year. 2. Why can't ligers live long ? A. Because their chromosomes are different. B. Because they are too small when they are born. C. Because their parents don't live long. D. Because they are short of food. 3. How many ligers did the passage mention? A. Three.         B. Four.          C. Five.         D. Six. 4. What is the best title of this passage? A. China's longest living twin ligers celebrate their lst birthday B. Why can't ligers in the world live long C. How to raise ligers safely D. The story behind the ligers