Use of English PRO

There is still no adequate (1) EXPLANATION (EXPLAIN) why, several thousand years ago, cultures in both Egypt and South America saw the (1) ............ (INTRODUCE) of pyramids. Was it coincidence? Many (2) ............ (SCIENCE) believe that it was, and state that there is no (3) ............ (POSSIBLE) at all that people from two distant continents traded information on (4) ............ (BUILD) techniques. However, some (5) ............ (REVOLUTION) theories in recent years, based on the (6) ............ (DISCOVER) that the two cultures also share key myths, legends and beliefs, suggest that the (7) ............ (APPEAR) of pyramids on opposite sides of the world was no coincidence at all. One (8) ............ (RESEARCH) working on this, Crystal Davis, said: 'The importance of finding out the truth here cannot be exaggerated. It could change our whole understanding of the history of the world.'