Fiber-optic cables rely on total internal reflection

Which of these is most responsible for differences between the twentieth century to the twenty-first century?

Donnie does not have powerpoint. which method would be best for elana to save and share her presentation as is? a pdf a doc an rtf a ppt

The best definition of an idiom is a. a word or phrase that describes a noun b. a word or phrase describing a verb c. a phrase containing figurative language in which the word expresses a different idea from its exact meaning d. a phrase that compares two unlike objects or ideas