三条直线l1:x-y=0,l2:x+y-2=0,l3:5x-ky-15=0能构成三角形. (1)k≠5. (2)k≠-5.
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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