Q: In this task, you will use your knowledge about language (and common sense) to determine what element the marked number refers to. The numbers are marked with two underlines around them, like: _ number _. Your answer should be chosen from the given text, and should not contain other words.
Carl Sagan:  There are some hundred billion galaxies , each with , on the average , a hundred billion stars , 1011 x 1011 = 1022 , _ ten _ billion trillion . In the face of such overpowering numbers , what is the likelihood that only one ordinary star , the Sun , is accompanied by an inhabited planet ? Why should we , tucked away in some forgotten corner of the Cosmos , be so fortunate ? To me , it seems far more likely that the universe is brimming over with life . But we humans do not yet know . We are just beginning our explorations . From eight billion light - years away we are hard pressed to find even the cluster in which our Milky Way Galaxy is embedded , much less the Sun or the Earth . The only planet we are sure is inhabited is a tiny speck of rock and metal , shining feebly by reflected sunlight , and at this distance utterly lost .
A:
stars