Complete the following summary of the paragraphs of Reading Passage, using NO MORE THAN THREE WORDS from the Reading Passage for each answer.
Write your answers in boxes.

The reason why had big size mammals become extinct 11,000 years ago is under hot debate. First explanation is that [1] of human made it happen. This so called [2] began from 1960s suggested by an expert, who however received criticism of lack of further information. Another assumption promoted by MacPhee is that deadly [3] from human causes their demises. However his hypothesis required more [4] to testify its validity. Graham proposed a third hypothesis that [5] in Pleistocene epoch drove some species disappear, reduced [6] posed a dangerous signal to these giants, and [7] finally wiped them out.