Check the Following Paragraphs for Unity

Check the following paragraphs for unity. Select the number of the sentence that does not belong in the paragraph. (1) One of the great mysteries of archeology, the study of past human life and culture, is the Nazca Lines. (2) In the desert south of Lima, Peru, these lines form drawings so huge that they are best viewed from an airplane. (3) Depicting enormous hummingbirds, monkeys, whales, spiders, and geometric shapes, these lines were scratched into the earth over a thousand-year period from 500 BC to 500 AD. (4) Since their "discovery" by a pilot in the 1930s, scientists have struggled to understand their meaning. (5) Some researchers believe that the Nazca lines served a spiritual purpose and were a way to communicate with the gods. (4) Many others claim that the lines predicted seasonal changes and other astrological events. (5) Some believe that the lines pointed to precious sources of water. (6) The mystery of the crystal skulls is another great mystery of archeology. (7) The most far-fetched theory about the Nazca lines is that they sent messages to space aliens and provided runways where ships from outer space could land.

A) sentence 3
B) sentence 6
C) sentence 7