这种感染是由肺部的细菌引起的。

The infection was caused by ___bacteria in the lung.

我们很幸运，在那段时间，天气寒冷，低温阻止了细菌的传播。

We were just lucky that during that period, the weather was cold and low temperatures prevented ___bacteria from spreading.

科学家正在研究如何控制环境中的有害细菌。

Scientists are researching how to control harmful ___bacteria in the environment.