The correct answer is: A. The manipulation of variables.
An experimental study is a type of research that involves manipulating one or more variables to observe the effect on another variable. The manipulated variable is called the independent variable, and the variable that is observed is called the dependent variable. The goal of an experimental study is to determine whether there is a cause-and-effect relationship between the independent and dependent variables.
Option B, conceptual parameters, is incorrect because conceptual parameters are not manipulated in an experimental study. Conceptual parameters are the concepts that are being studied in the research. For example, in a study on the effects of sleep deprivation on memory, the conceptual parameters might be sleep deprivation and memory.
Option C, replication of research, is incorrect because replication of research is not the same as conducting an experimental study. Replication of research involves repeating a study that has already been conducted to see if the results are the same.
Option D, survey of literature, is incorrect because a survey of literature is not the same as conducting an experimental study. A survey of literature involves reviewing the existing research on a topic to identify what is already known and what needs to be studied further.
In conclusion, the correct answer is: A. The manipulation of variables.