我国第二、三级阶梯的分界线以____________岭、________山脉、________山、_________山为界。
大兴安 太行 巫 雪峰
Only when you are old enough ________ that you didn't make most of your time. [ ]
A. you will realize
B. will you realize
C. have you realized
D. do you realize
植物病原物侵入寄主的途径有（）、（）和（）。
