Final answer:
The true characteristic of all experiments is that they contain independent and dependent variables. While blind assignments, equal group numbers, and ethical use of deception might be present in many cases, they are not definitive features.
Step-by-step explanation:
True Characteristics of All Experiments
Of the options provided, the statement that is true of all experiments is that they have independent and dependent variables. The independent variable is the one that is manipulated or controlled by the researcher to observe its effect on the dependent variable, which is the outcome that is measured. While blind assignments and equal group sizes are common in many experiments, they are not mandatory characteristics of an experiment. For instance, participant blinding is used to prevent bias, but it's not a feature of every experiment. Similarly, having equal numbers of participants in the experimental and control groups can help in the analysis but is not always feasible or required.
Experiments do not necessarily have to involve deception. However, when used, deception must always be ethically justifiable and participants must be debriefed afterwards. Random assignment to treatment groups is a key characteristic to eliminate the impact of lurking variables and to ensure that group differences are due to the manipulation of the independent variable and not other factors.