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This is a very philosophical question and not very well formulated.
"A scientist should not let their research and study be influenced by any external factor besides the variables in study".
All of the above can be external factors of an study about change of the volume of a gas when we change the temperature. But at the same time they all can be variables if the scientist is studying the relationship between gender and practice of religion. In this last case the Temperature and the volume of the gas will be external factors that the researcher has to avoid to influence his study.
There are some genetic diseases that are more frequent in some ethnics groups than others, if the scientist is studying the correlation of that disease and the ethnicity, it will be influencing the results of studies.
Nationality it is a little more difficult to determine sometime in a scientific study, but also a scientist can be studying the correlation in the migrations of Italian people in America, looking at records of persons arriving to the country with a specific nationality.
The last one definitely
Religion and science are "enemies" I'm religious but you don't mix those two together when doing experiments and researches. But I agree with Cuanchi, this is a debatable question.