If \[x=a{{t}^{2}},y=2at\], then \[\frac{{{d}^{2}}y}{d{{x}^{2}}}=\] [Karnataka CET 1993]

• A. \[-\frac{1}{{{t}^{2}}}\]
• B. \[\frac{1}{2a{{t}^{3}}}\]
• C. \[-\frac{1}{{{t}^{3}}}\]
• D. \[-\frac{1}{2a{{t}^{3}}}\]