已知ab＝－1，a＋b＝2，则式子a2＋ab＋b2＝＿＿＿＿＿。
5
∵ab＝－1，a＋b＝2
∴a2＋ab＋b2＝(a+b)2-ab=4+1=5
.
Though the teacher had tried to make the problem easy__________, still Lily and her partner were at a loss.
A．understood
B．understanding
C．to understand
D．to be understood
看板的种类有许多种，常见的形式有______
A．零件箱看板
B．卡片
C．标准容器
D．小圆球看板
E．指示灯
