【单选题】
正四棱锥底面边长是2,高是1,则斜高是()
①
<img class="kfformula" src="20190809/1565327137897917.png" data-latex="\sqrt {2}"/>
②
<img class="kfformula" src="20190809/1565327137411071.png" data-latex="\sqrt {5}"/>
③
<img class="kfformula" src="20190809/1565327137707931.png" data-latex="2"/>
④
<img class="kfformula" src="20190809/1565327137840495.png" data-latex="\sqrt {3}"/>