设集合A = {1, a }，则P(A) = (    )．

、{{1}, {<em>a</em>}, {1, <em>a</em> }}

、{{1}, {<em>a</em>}}

{<img style、"vertical-align: middle;" src="http://hebei.ouchn.cn/pluginfile.php/19780/question/answer/1207020/3/48784/006%20%281%29.gif" alt="" width="17" height="19">,{1}, {<em>a</em>}}

{<img style、"vertical-align: middle;" src="http://hebei.ouchn.cn/pluginfile.php/19780/question/answer/1207020/3/48785/006%20%281%29.gif" alt="" width="17" height="19">,{1}, {<em>a</em>}, {1, <em>a</em> }}