Which explanation is most likely the reason for the evolution of a larger brain in humans?
the size of the human brain increases the more it is used.
a larger brain allows humans to solve complex problems.
the size of the human brain has changed randomly over time due to mutations.
a large brain increases humans’ ability to fight and survive disease.

You are given an electron micrograph of a bacterial cell. in the micrograph you can clearly see three thin layers of different densities surrounding the cell. based on the micrograph, you can infer that this cell is and would appear after application of the gram stain procedure. gram-negative / pink gram-positive / purple gram-positive / pink gram-negative / purple