如下方程为非线性的是() A、y=3r(t);B、y''(t)+2ty'(t)+3y(t)=r(t);C、y''(t)+2y(t)y'(t)+3y(t)=r(t);D、y''(t)=3y(t) 发布时间:2024-09-25 11:03:32