单项选择题

"Time cannot be added to a person’s life, but it can be made more valuable by avoiding waste. " This was the philosophy of a man who devoted most of his time to the creation of new plants: Luther Burbank, the plant magician.
Burbank has been called the plant magician because he could do things with plants which were as amazing as the tricks of a magician. He truly astonished the world with his achievements in the development of many kinds of plants, such as giant fruits with new flavors and trees which grew faster than their ancestors. These, and many more achievements, were of great economic value and benefit to people all over the world.
In his lifetime of seventy-seven years Burbank became an American legend. He began life in 1849 on a farm in the state of Massachusetts. It was the same year that men across the continent in California discovered gold, that precious metal so eagerly sought after in the earth. Eventually Burbank would follow them. But he would spend his life drawing a different treasure from the same California earth: a wealth of new plants and fruits.
The Massachusetts countryside may have provided young Burbank with a feeling for the mysteries of nature, but his scientific training came during the visits of an uncle who was a scientist. Through his uncle, Luther met the famous naturalist, Louis Agassiz. Agassiz introduced him to the complicated process by which plants grow, such as the steps in the making of seeds from pollen (花粉) carried by insects, by birds, by the very winds of the field. Attracted by the ways of nature, Burbank took his first steps into the work that was to occupy his whole life. In his life, Luther Burbank ______.