Things have changed a lot ____ I wrote to you last time.

A．when

B．since

C．as

D．before

遇到呼吸、心跳骤停的伤病员，现场可采用什么方法急救？（）

A.人工呼吸

B.胸外心脏按压

C.挂盐水

D.吸氧气