Some you wouldn't see by stepping outside, but it gives you a general understanding of what you should be looking for.
Hope this helps!
Resazurin cell viability assay is a simple, rapid, reliable, sensitive, safe and cost-effective measurement of cell viability.
https://www.creative-bioarray.com/support/resazurin-cell-viability-assay.htm
Answer:
A) it binds to a protein called haemoglobin in red blood cells
Explanation: