1. When $k$ takes any real number, the vertex of the parabola $y=\frac{4}{5}(x-k)^{2}+$ $k^{2}$ lies on the curve ( ).
(A) $y=x^{2}$
(B) $y=-x^{2}$
(C) $y=x^{2}(x>0)$
(D) $y=-x^{2}(x>0)$
(2004, National Junior High School Mathematics Competition Hubei Province Preliminary Contest)
(Answer: A. )