A
句意：根据短文，下列哪个选项是正确的?
A. 科学家们仍在努力改进这种酶。
В. 这种酶会污染大面积的土地和水。（文章没提到）
C. 天然酶比改良酶更有效。（和文章说法相反）
D. 天然酶对人和动物有害。（文章没提到）
根据文章倒数第二段第1-2行：
John McGeehan, one of the lead researchers, said, "We've made an improved enzyme. It's better than the natural one. And we are trying to make more improvements to it."
首席研究员之一约翰·麦吉汉说：“我们已经制造出了一种改进的酶。它比天然的好。我们正在努力对它进行更多的改进。”
以及最后一段：
The team is now trying to make the enzyme break down PET in large quantities. "We'll see that the plastic pollution may be stopped with this technology. However, there is still a long way to go," John McGeehan added.
该团队现在正试图让这种酶大量分解PET。“我们将看到，这项技术可能会阻止塑料污染。然而，还有很长的路要走，”约翰·麦吉汉补充道。
可知，科学家们仍在努力改进这种酶。
故选A
