Question

    This was not an easy task. The reason1.this was difficult was that the team had limited resources. They did not have enough staff, and the laboratory in which they 2.(work)had poor air quality. However, after hundreds of failed experiments, they eventually came across a promising chemical. It worked well in experiments on animals,3.they had to know if it was safe for humans. Tu Youyou bravely volunteered to be the first human subject when they were ready to start testing and the rest of her team followed her.

Answer

1.why

2.worked

3.but

【解析】

这是一篇说明文。文章主要说明了屠呦呦实验困难的原因。然而，经过数百次失败的实验，他们最终发现了一种很有前途的化学物质。在动物实验中效果很好，但他们必须知道它对人类是否安全。当他们准备开始测试时，屠呦呦勇敢地自愿成为第一个人体实验对象。

1.

考查关系副词。句意：这之所以困难的原因是团队的资源有限。结合句意表示“……的原因是……”固定句型为the reason why…is/was that…。why引导的定语从句。故填why。

2.

考查动词时态。句意：他们没有足够的员工，而且他们工作的实验室空气质量很差。work在从句中作谓语，且根据上文They did not have enough staff可知应用一般过去时。故填worked。

3.

考查连词。句意：在动物实验中效果很好，但他们必须知道它对人类是否安全。结合上下文语境可知此处为转折关系，应用连词but。故填but。