单选题 e(t)为激励,r(t)为响应,LTI系统的微分方程为r''(t)+7r'(t)+10r(t)=e''(t)+6e'(t)+4e(t),初值条件为r(0-)=0.8,r'(0-)=0,f(t)=-2u(t),则初始状态r'(0+)=( )