1. Visual indicators can be described as those markers that give visible signs.
- The signs could be in the form of a color change.
2. Chemical indications are substances that change due to the presence or the absence of chemicals such as acids or alkali.
3. Physical indication are the changes that can be easily seen in a body through examination.
4. Biological indications are organisms in an environment whose characteristics shows that there are certain environmental conditions present.
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