科学家们正在努力为这种疾病研发疫苗。

___Scientists are working to create a vaccine for the disease.

美国国家航空航天局昨天承认，他们将在未来两年内派遣一组训练有素的科学家前往火星。

NASA admitted yesterday they will send a group of highly trained ___scientists to Mars in the next two years.

我的朋友是研究气候变化的科学家。

My friend is a ___scientist who studies climate change.