I do think the North Koreans are testing the US response.

我确实认为朝鲜是在试探美国的反应。

Culturing cells allowed scientists to test their response to all kinds of drugs, diseases, and conditions in order to understand how the human body would react.

培养细胞使科学家能够测试它们对各种药物、疾病和条件的反应，以了解人体会如何反应。