Etymology is the study of:
a. language
b. plants
c. animals
d. words

d. words

Explanation:

The etymology is the study of history of words. More elaborately it can be define as the means of origin of a particular word. It recognizes a fact that a word has come from a limited basic mechanisms, the changes occurring in a language, and borrowing of a particular word from a different linguistic set.

a community that experiences major changes undergoes progress

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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.