Scientific investigations most often start from observations of the natural world and which of the following?
a) model
b) computers
c) variable
d) questions

The answer should be D.) Questions

because of this, scientists use the scientific method for observations they discover.

all answers true and false

explanation:

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what do the different brain waves do?

explanation:

brainwaves are produced by synchronised electrical pulses from masses of neurons communicating with each other. brainwaves are detected using sensors placed on the scalp. brainwave speed is measured in hertz (cycles per second) and they are divided into bands delineating slow, moderate, and fast waves.