二次型<imgwidth="210"height="28"v:shapes="_x0000_i1315"src="http://wljy.whut.edu.cn/uploadfiles/word/xxds05.files/image375.png">的规范形是()
①
<imgwidth="68"height="28"v:shapes="_x0000_i1316"src="http://wljy.whut.edu.cn/uploadfiles/word/xxds05.files/image377.png">
②
<imgwidth="22"height="28"v:shapes="_x0000_i1317"src="http://wljy.whut.edu.cn/uploadfiles/word/xxds05.files/image379.png">
③
<imgwidth="58"height="28"v:shapes="_x0000_i1318"src="http://wljy.whut.edu.cn/uploadfiles/word/xxds05.files/image381.png">
④
<imgwidth="58"height="28"v:shapes="_x0000_i1319"src="http://wljy.whut.edu.cn/uploadfiles/word/xxds05.files/image383.png">