A:未加盐酸时:c(OH﹣)>c(Na+)=c(NH3•H2O)
B:加入10mL盐酸时:c(NH4+)+c(H+)=c(OH﹣)
C:加入盐酸至溶液pH=7时:c(Cl﹣)=c(Na+)
D:加入20mL盐酸时:c(Cl﹣)=c(NH4+)+c(Na+)
同一平面内两圆的半径是R和r,圆心距是d,若以R、r、d为边长,能围成一个三角形,则这两个圆的位置关系是( )
David his friend's invitation to the picnic in order to stay at home and study for the test.