样本判定系数R2的计算公式是（　　）。

A、_{<IMG src="http://admintk.100xuexi.com/UpLoadImage/2013-05-07/23083eee-b46a-4b8d-8b32-845e5f591097.gif" width="63" height="39">}

B、_{<IMG src="http://admintk.100xuexi.com/UpLoadImage/2013-05-07/18404bff-c1ed-4784-abb3-143864e57aab.gif" width="63" height="39">}

C、_{<IMG src="http://admintk.100xuexi.com/UpLoadImage/2013-05-07/fff1b551-a2b0-4d49-abb2-49252201647b.gif" width="81" height="39">}

D、_{<IMG src="http://admintk.100xuexi.com/UpLoadImage/2013-05-07/97efaa49-dec8-46c7-8081-4a533a0bd60c.gif" width="63" height="39">}