What was nikola tesla contribution to electricity?

Explanation:

Nikola Tesla was a Serbian-American engineer and inventor who is highly regarded in energy history for his development of alternating current (AC) electrical systems. He also made extraordinary contributions in the fields of electromagnetism and wireless radio communications.

- "schenck v. united states, case in which the u.s. supreme court ruled on march 3, 1919, that the freedom of speech protection afforded in the u.s. constitution's first amendment could be restricted if the words spoken or printed represented to society a “clear and present danger.” "

- speech aimed to potentially create danger could be banned.

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answer; /// i believe that the correct answer is (d)the huang he river valley;