题目

Our lifestyles today are very busy. We have family, school, sports, entertainment and social activities to fit into a time that seems never enough. We need to be healthy to meet the demands of daily life. But what does it mean to have a healthy lifestyle? To have a healthy lifestyle, we need to: ◆ eat different kinds of healthy food most of the time ◆ do exercise often ◆ have time to relax ◆ get enough sleep to give our bodies time to grow healthy and strong Read about a normal day in the lives of two children. Abbey gets up at 7:00 am, feeds the dog, and has cereal and a gl下列命题中，错误的是（ ）A．关于x的方程x2=k必有两个互为相反数的实数根B．关于x的方程（x-c）2=k2必有两个实数根C．关于x的方程ax2+bx=0必有一根是零D．关于x的方程x2=1-a2可能没有实数根