题目

Since no other way to escape from the flood, ____ only safe thing is to take ____chance. A．an ; 不填        B．the ; a          C．an; a          D．不填；the 答案：B下列方程中，是一元二次方程的是（ ）A．5x+3=0B．x2-x（x+1）=0C．4x2=9D．