RPI卡环组包括（）。
A.近中鸦支托
B.远中邻面板
C.颊侧Ⅰ型杆式卡环
D.长臂卡环
E.连续卡环
参考答案：A, B, C
下列属于自然因素对生态平衡的影响是（ ）
A．海南毒豇豆
B．修建大型工程
C．引进水葫芦
D．玉树地震
It ________ we had stayed together for a couple of weeks _________ I found we had a lot in common. [ ]
A. was until; when
B. was until; that
C. wasn't until; when
D. wasn't until; that
