The correct answer is b) observable.
Science is fundamentally concerned with studying and understanding the natural world through observation and experimentation. This means that scientists develop hypotheses and conduct experiments that yield results which can be observed, measured, and tested. While scientific inquiry can involve concepts that may be considered ‘indisputable’ or ‘variable’, the core of the scientific method relies on observations that can be repeated and verified by others.
Additionally, while science often addresses living organisms, it is not restricted to the study of life alone. Therefore, the emphasis on observable phenomena is crucial, as it allows scientists to gather evidence and build knowledge based on what can be seen and tested, forming the basis for scientific theories and laws.