描述逻辑电路的真值表见表所示,则其逻辑表达式F=______。<imgwidth="595"height="147"src="http://wljy.whut.edu.cn:80/uploadfiles/word/szlj01.files/szlj013324.png">
①
<imgwidth="89"height="33"src="http://wljy.whut.edu.cn:80/uploadfiles/word/szlj01.files/szlj013327.png">
②
<imgwidth="79"height="37"src="http://wljy.whut.edu.cn:80/uploadfiles/word/szlj01.files/szlj013330.png">
③
<imgwidth="52"height="27"src="http://wljy.whut.edu.cn:80/uploadfiles/word/szlj01.files/szlj013333.png">
④
<imgwidth="58"height="29"src="http://wljy.whut.edu.cn:80/uploadfiles/word/szlj01.files/szlj013336.png">