原式=1xx+1·x+1
若代数式x2+3x+5的值为7,则代数式3x2+9x﹣2的值等于( )
Many people miss Lei Feng because he was so ____ (help).
与吸入的气体相比,人呼出气体中氧含量减少,二氧化碳含量增加,其根本原因是( )