W} D.{3-23} E. None of these 7.x2-0.4x+k is a perfect square if k=………. A. 0.4 B. 0.04 C.-0.04 D.-0.4 E. 0.2 x2-6x+k=(x+2)2, then A. k=3,a=-3 B. k=9,a=3 C. k=-9,a=-3 D. k=9,a=-3 E. k=3,a=9 x2+8x+10+k is