同时包含a12和a21的项是a12a21a33a44a12a21a34a43只包含a12不包含a21的项是a12a23a31a44a12a23a34a41a12a24a31a43a12a24a33a41只包含a21不包含a12的项是a13a21a32a44a13a21a34a42a14a21a32a43a14a21a33a42
前三个字是什么?*四所?