填空题

Life on earth depends on the sun. Day after day we see its light and feel its (36) , but we do not often know or (37) the birth or the beginning of their (38) . Yet there are amount of (39) things about the sun. One is its distance from the earth. This is about ninety-three (40) miles. It is to us, a long distance. A (41) of this distance, even if it could be made, would take (42) hundred years even in the (43) rocket.
The sun makes us feel heat, even at a distance of ninety-three million miles. This is not surprising. (44) . But we receive only a small part of this heat. The total heat of the sun could melt a column of ice two and a quarter miles thick and ninety-three million miles high in one second.
The brightness of the sun is equally astonishing. As we said earlier, we receive only a very small part of the sun’s heat. (45) This is sufficient for the growth of trees and plants, and for the existence of living creatures on earth. (46) . The heat and light from the sun come in just the right quantities for life on earth.