题目内容

3x-4y的最大值为12． (1)实数x，y满足方程x2+y2=4． (2)实数x，y满足方程x2+y2-4x-2y+1=0．

A. 条件(1)充分，但条件(2)不充分
B. 条件(2)充分，但条件(1)不充分
C. 条件(1)和(2)单独都不充分，但条件(1)和条件(2)联合起来充分
D. 条件(1)充分，条件(2)也充分
E. 条件(1)和(2)单独都不充分，条件(1)和条件(2)联合起来也不充分

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