氨茶碱治疗心源性哮喘主要机制是( )
A.降低血压
B.强心利尿
C.扩张支气管
D.扩张外周血管
E.兴奋中枢
参考答案:B
解析: 氨茶碱治疗心源性哮喘的主要机制为强心利尿作用。
在队列研究中,对关联强度进行统计学检验的无效假设是()。
A.RR=0
B.RR=1
C.RR>1
D.RR<1
E.BR>0
Some farmers have _____ keeping deer, and there are now about 4,500 deer farms in the country.[ ]
A. turned to
B. turned into
C. turned up
D. turned down