题目(单选题,4分)函数f(x,y)=x^3+3xy^2在点(1,1)处的梯度为( )A. 5i+5jB. 6i-6jC. 5i-5jD. 6i+6j(单选题,4分)函数$f(x,y)=x^{3}+3xy^{2}$在点(1,1)处的梯度为( )A. 5i+5jB. 6i-6jC. 5i-5jD. 6i+6j题目解答答案D. 6i+6j