Which best describes a dichotomous key? Each step has two choices.
Each step can have any number of choices.
Each step describes two possible inferences.
Each step is based on genetic traits.

they deliver oxygen to the blood

evidence and logical support is essential for a scientist to do in order to maintain credibility. this is because no one can believe without any logic and without any evidence.hence a scientist can maintain credibility by proving himself and by answering logically so experiments prove very beneficial. logical hypothesis give conclusion which is acceptable. therefore, there are two main factors to maintain credibility by a scientist is evidence and logical support.