如图,BD、CE相交于点A,下列条件中,能推得DE∥BC的条件是( )
A:AE:EC=AD:DB
B:AD:AB=DE:BC
C:AD:DE=AB:BC
D:BD:AB=AC:EC
—How about _______ in the river with us?
—Sorry, I can't. My parents often tell me _______ that.
下列各项与肺泡内的气体交换无直接关系的是( )
某同学用导线把一个开关和一个灯泡接在一节干电池的两极上,当他断开开关时,小灯泡亮了;当他闭合开关时,小灯泡就不亮了.下列分析中正确的是( )