A:and he
B:when he
C:that he
D:he
我国第一级阶梯与第二级阶梯的地理界线是( )
How many ______?
青少年难以经受网上负面效应,诱惑,产生了许多令人担忧的____。
Yesterday an old man's house was _______fire. And now he is_______ hospital.