—It's a long time ________ I saw you last.
—Yes,and what a pity!It will be a long time ________ we see each other again.
A:since; before
B:when; when
C:since; when
D:before; since
若fx=-x+3a,x<0ax,x≥0(a>0且a≠1),在定义域R上满足fx2-fx1x1-x2>0,则a的取值范围是( )
不属于哺乳动物特有的特征是( )
有一位干部退休后,情绪低落,精神不振,疾病缠身,久治不愈。后来到老年大学学练书法,从中找到了乐趣,心情舒畅了,身体也健康多了。这一事实说明( )