设A为3×4矩阵，B为4×3矩阵，则下列运算可以进行的是（    ）.

<em><span style、"font-family: 'times new roman', times, serif;">A+B</span></em>

<em><span style、"font-family: 'times new roman', times, serif;">AB</span></em>

<em><span style、"font-family: 'times new roman', times, serif;">B+A</span></em>

<em><span style、"font-family: 'times new roman', times, serif;">BA'</span></em>