设z=sin(x2-y2)，则∂2z/∂x2=()

设z=sin(x²-y²)，则∂²z/∂x²=()
A、-sin(x²-y²)
B、sin(x²-y²)
C、-4x²sin(x²-y²)
D、-4x²sin(x²-y²)+2cos(x²-y²)
【正确答案】：D
【题目解析】：∂z/∂x=2xcos(x²-y²)，∂²z/∂x²=2cos(x²-y²)-4x²sin(x²-y²)．