图9+++++++++++++++++++++++++++++++++++++++++++++++++++2+2+2+2+2++2+2+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++2+2+2+2+2+2+2+2++++2+2+++++2+++++2+2+2+++++2+++++2+2+++++2+2++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++