Fill in the blank (iii).

Directions: Read the following passage having some numbered blanks.

Of all the countless things my son and I learned from the professor, the meaning of the square root was ____(i)____ the most important. No doubt he would have been bothered by my use of the word countless — too sloppy, for he believed that the very origins of the universe could be explained in the exact language of numbers — but I don't know how ____(ii)____ to put it. He taught us about enormous prime numbers with more than a hundred thousand places and the largest number of all, which was used in mathematical proofs and was in the 'Guinness Book of Records' and about the idea of something beyond infinity. As ____(iii)____ as all this was, it could never match the experience of simply spending time with the professor. I ____(iv)____ when he taught us about the spell cast by placing numbers under this square root sign. It was a rainy evening in early April. My son's schoolbag ____(v)____ abandoned on the rug; the light in the professor's study was dim. Outside the window, the blossoms on the apricot tree were heavy with rain.