Yuan Longping, born and ____ (bring) up in China, is a leading figure in the rice-growing world. When he was a boy, he ____ (educate) in many schools, and was given the nickname, “the student ____asks questions.”

    He was interested in plants from an early age, and he studied agriculture in college. As a young teacher, he began ____(experiment) in crop breeding. He thought there was only one way ____ (have) more rice quickly. That was to cross different species of rice plant. Then he began his search for a ____ (specially) type of rice plant. It had to be male and sterile. When the naturally sterile male rice plant was discovered in 1970, it was ____ breakthrough. As a result, China's rice production rose____ 47.5% in the 1990's. And 50 thousand square kilometers of rice fields were converted to ____ (grow) vegetables and other cash crops. ____(follow) this, Yuan Longping's rice was exported to some other countries.

下列描述的一定是金属元素的是（　　）