老师能否翻译一下A选项是什么意思

问题如下：

Question The conditional expected value of a random variable is best described as the:

选项：

A.expected value of a random variable given an event or scenario.

B.probability-weighted average of the possible outcomes of the random variable.

C.weighted average of the probabilities of an event given all possible scenarios.

解释：

A is correct. The conditional expected value of a random variable is the expected value of a random variable given an event or scenario.

B is incorrect because an expected value (not a conditional expected value) is defined as the probability-weighted average of the possible outcomes of the random variable.

C is incorrect because an expected value is not a probability. This answer defines the total probability rule, which is the weighted average of the probabilities of an event given all possible scenarios.