设区域D由曲线围成，则

儿童的身高和体重的相关情况呈现为()。

袋中有 3 个红球， 2 个白球，第一次取出一球后放回，第二次再取一球，则两球都是红球的概率是 ( )

设下列函数的定义域均为（－∞，＋∞），则其中可作为概率密度的是（）

下面分数中，是最简分数的是()

管理成功的秘诀在于()。

We are all concerned _______ her safety.

设3阶实对称矩阵A的特征值分别为2,1,0，则()

With the publication of( ),Theodore Dreiser was launching himself upon a long career that would ultimately make him one of the most significant American writers of the school later known as literary naturalism.

Look at this group of people ______ beach volleyball.