用英语写一篇60词的短文，介绍你最好的朋友 My best friend is Tommy.He is fourteen this year.His is an American，but he is currently studying in China.His favourite food is dumplings as it tastes really good.Tommy's studies are great and he.
化简√(a+2√a-1)+√(a-2√a-1) （a≥1）谢谢了， [a+2√(a-1)]+√[a-2√(a-1)]=√[(a-1)+1+2√(a-1)]+√[(a-1)+1-2√(a-1)]=√[√(a-1)+1]^2+√[√(a-1)-1]^2=√(a-1)+1+√(a-1)-1=2√(a-1)or=√(a-1)+1+1-√(a-1)=2
当手扶拖拉机的柴油机出现故障而使转速急剧增加，正常操作已经不能使它转动（这种故障叫做“飞车”）时，下列应急措施中可行的是那一个？
