Answer:
To test the presence of protein in the food substance which gives a blue-to-purpule colour
Holmes said to Watson "My dear doctor, this is a time for observation, not talk, because it was part of his method to observe closely and then to consider his observations. The correct answer is A.
Yes, this is true, and it is actually one of the organisms driving evolution! Some organisms develop mutations that are actually beneficial (better eye-sight, for example) and they're more likely to pass those to their children that individuals without those mutations!
