How many full-length strands of hair are collected from the scalp to use as a sample?
2
15
25
50

I think the correct answer from the choices listed above is the last option. It would be 50  full-length strands of hair are collected from the scalp to use as a sample. The more sample the better because you can easily repeat an experiment if there are errors found. Hope this answers the question.

It would be the equator.