Complete the following sentence with a (compound) word derived from the one(s) given in bracket.
Natural （ ） ensures only the fittest survive to pass their genes on to the next generation.(select)
【正确答案】：SELECTION
【题目解析】：
Natural selection自然选择，物竞天择说。句意：自然选择确保只有适者生存才能将基因传给下一代。