In       18-minute address to students across America on September 8, 2009, President Obama told American students to make          most of their education．

A．an; the

B．an; a

C．the; the

D．the; a

慢性支气管炎发作期治疗关键在于

A．祛痰
B．平喘
C．镇咳
D．控制感染
E．吸氧