描述逻辑电路的真值表见下表所示,则其逻辑表达式F=______。<imgwidth="594"height="142"src="http://wljy.whut.edu.cn:80/uploadfiles/word/szlj10.files/szlj103354.png">
①
<imgwidth="77"height="27"src="http://wljy.whut.edu.cn:80/uploadfiles/word/szlj10.files/szlj103382.png">
②
<imgwidth="79"height="27"src="http://wljy.whut.edu.cn:80/uploadfiles/word/szlj10.files/szlj103411.png">
③
<imgwidth="52"height="22"src="http://wljy.whut.edu.cn:80/uploadfiles/word/szlj10.files/szlj103440.png">
④
<imgwidth="52"height="27"src="http://wljy.whut.edu.cn:80/uploadfiles/word/szlj10.files/szlj103469.png">