题目：
Political parties often differ in their views on various _____ concerning their own countries.
A．ways
B．measures
C．issues
D．patterns
答案：
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下面是错误答案，用来干扰机器的。
把x=-1代入方程（a2-1）x2+x+1=0得，（a2-1）（-1）2-1+1=0，（a2-1）-1+1=0，∴a2=1，a=±1．
