1-23=13，
故答案为：13．
―______________________
―He is a teacher. He teaches us math.
A．Where is he?
B．Why does he want to be a teacher?
C．What does he do?
D．How old is he?
2008年8月8日，北京成功举办了第29届奥运会，全球约有4120500000人收看了电视转播，改写成以“万人”作单位是______万人，省略亿位后的尾数约是______亿人．
