已知变量a、b已被赋值，要交换a、b的值，采用的算法是（   ）

A．a =" b," b =" a"

B．a =" c," b =" a," c =" b"

C．a =" c," b =" a," c =" a"

D．c =" a," a =" b," b = c

支气管扩张最有意义的体征是（）

A.贫血

B.杵状指

C.固定的局限性湿啰音

D.消瘦

E.多变的哮鸣音