204. Old people think fondly of old times. They often gather and _____ old friend and events.

A．look forward

B．look back on

C．look back

D．look into

导致休克肺的原因包括()

A．输液、输血过量

B．表面活性物质缺乏

C．肺微血管栓塞

D．肺小静脉收缩