单纯型慢支和喘息型慢支主要区别在于
A．咳嗽轻重
B．咳痰是否反复带血
C．喘息的轻重
D．是否有喘息
E．肺部湿罗音
参考答案：D
Not only should you get used ______ under difficult conditions but you also you pay more attention ______ your work well.
A．to work, to do
B．to working, to doing
C．to work, to doing
D．to working, to do
企业质量管理体系获准认证的有效期为( )年。
A．一
B．二
C．三
D．四
