Which of the following statements is true? a. Destruction of a cell under the action of radioactive rays is random variable. D b. By a random event related with a certain experiment we understand any event which occurs in every trial. D c. None of the above. D d. Probability theory-the section of mathematics studying laws of the casual phenomena.

The correct answer is:<br /><br />d. Probability theory - the section of mathematics studying laws of the casual phenomena.<br /><br />Explanation:<br /><br />a. Destruction of a cell under the action of radioactive rays is a random event, not a random variable. A random variable is a numerical quantity that can take on different values depending on the outcome of an experiment.<br /><br />b. A random event related to a certain experiment is an event that can occur with a certain probability, but not necessarily in every trial. It is not defined by its occurrence in every trial.<br /><br />c. "None of the above" is not the correct answer since option d is true.<br /><br />d. Probability theory is indeed the branch of mathematics that studies the laws of casual phenomena. It deals with the quantification of uncertainty and the analysis of random events.