第一节、完形填空（共15小题；每小题2分，满分30分）
阅读下面短文，掌握其大意，然后从1~15各题所给的A、B、C和D项中，选出最佳选项，并在答题卡上将该项涂黑。
How long can human beings live? Most scientists who study old age think that the human body is ___1___ to live no longer than 120 years. However, 110 years is probably the longest that anyone could hope to live —— if he or she is ___2___ healthy and lucky. Some scientists even say we can live as long as 130 years! Yet, our cells simply cannot continue to reproduce ___3___. They wear out, and as a result, we get old and ___4___ die.
