Respuesta :
Answer:
frontier; limitation
Explanation:
In science, a “frontier” research refers to a type of investigation at the limits of current knowledge, raising concerns about the existing methodology and often accompanied with a speculative hypothesis. In general, frontier research investigates a particular question/issue which is still controversial in the scientific community, thereby challenging the established paradigm. On the other hand, variables are those factors, traits, or conditions which can be measured and changed in an investigation/study. Many variables in a given study design represent an important limitation because they cause noise to establish an association with a particular outcome (in this case, methemoglobinemia disease). A scientific study involves at least one independent variable (i.e., the variable that is not changed during the study) and one dependent variable (i.e., the variable that is changed).
The missing words are Frontier and Limitation.
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