A:whe
B:before
C:that
D:Since
已知a>0,b>0,a+b=1,则1a+1b的取值范围是( )
若四次测量一本书的宽度记录为:12.38cm,12.36cm,12.38cm,12.34cm,则这本书宽度平均值是( )
i是虚数单位,复数z满足(1+i)z=2,则z的实部为____.