下列关于两种证券组合的机会集曲线的说法中，正确的是(
)。
A．曲线上的点均为有效组合&nBsp; &nBsp; &nBsp; &nBsp; &nBsp; &nBsp; &nBsp; &nBsp; &nBsp; &nBsp; &nBsp; &nBsp; &nBsp; &nBsp; &nBsp; &nBsp;&nBsp;
B．曲线上报酬率最低点是最小方差组合点&nBsp; &nBsp; &nBsp; &nBsp; &nBsp; &nBsp; &nBsp; &nBsp; &nBsp; &nBsp;
C．两种证券报酬率的相关系数越大，曲线弯曲程度越小&nBsp; &nBsp; &nBsp; &nBsp;&nBsp;
D．两种证券报酬率的标准差越接近，曲线弯曲程度越小