Question

experiments or observational studies in which only one variable is manipulated are described as independent dependent observed controlled

Explanation:

In experimental design, a controlled experiment (or study) is one where only one variable is manipulated (the independent variable) while others are kept constant to observe the effect on the dependent variable. "Independent" refers to the variable being manipulated, not the study type. "Dependent" is the variable being measured. "Observed" is about watching, not the design. So the term for studies with one manipulated variable is "controlled".

Answer:

controlled (the option in the red box, likely labeled as, for example, D. controlled if following typical multiple - choice labeling, but based on the context, the correct term is controlled)