A scientist measured a 1 µA current in an area of a human brain. Unlike current in metals which is carried by free electrons, the current in the brain is mainly carried by potassium ions. Each potassium ion has one unit of charge e. This current corresponds to the flow of how many potassium ions per second?
(a) 6×10⁵; (b) 6×10⁶; (c) 6×10⁸; (d) 6×10¹²; (e) 6×10¹⁸.