已知a、b、c分别为Rt△ABC（∠C=90°）的三边的长，则关于x的一元二次方程（c+a）x²+2bx+（c-a）=0根的情况是（　　）.

竖直放置的一对平行金属板的左极板上用绝缘线悬挂了一个带正电的小球，将平行金属板按图所示的电路图连接。绝缘线与左极板的夹角为θ。当滑动变阻器R的滑片在a位置时，电流表的读数为I₁，夹角为θ₁；当滑片在b位置时，电流表的读数为I₂，夹角为θ₂，则 （     ） 
 

    “Early to bed, early to rise, makes a man healthy, wealthy(财富) and wise (智慧).”

    This is an old English saying (谚语)．Did you hear of it? It means that we must go to bed early and ____ up early in the morning．Then we will keep ____．We'll also be rich and clever.

    This is true．The body must have ____ sleep to be healthy．Children of young age should have ten ____ sleep every day．Children who don't have enough sleep can't do their work very well．They won't be clever and they may not become rich!

    The body also needs ____．Walking, running, jumping, swimming and playing games are all exercise．Exercise the body strong(强壮).

    Exercise also helps the blood(血) to ____ around inside the body．This is very important．Our blood ____ food to all parts(部分) of our body．The head also needs blood． Exercise helps us to think____.