He often stands against the fence and talks endlessly with my father _____ gardening problems. 

A．to

B．too

C．about

D．off

缺氧的概念是()

A．血液氧含量过低

B．血液氧容量降低

C．吸入气体氧分压降低

D．血液氧饱和度降低

E．供氧不足或用氧障碍