Which of the following electronic configurations is correct?

• A
  $K = [Ar]4s^1, Cr = [Ar]3d^44s^2, Cu = [Ar]3d^{10}4s^2$
• B
  $K = [Ar]4s^2, Cr = [Ar]3d^44s^2, Cu = [Ar]3d^{10}4s^2$
• C
  $K = [Ar]4s^1, Cr = [Ar]3d^54s^1, Cu = [Ar]3d^{10}4s^1$
• D
  $K = [Ar]4s^2, Cr = [Ar]3d^54s^1, Cu = [Ar]3d^{10}4s^2$