Answer the question from the given passage. Your answer should be directly extracted from the passage, and it should be a single entity, name, or number, not a sentence.

Passage: The Doctor rarely travels alone and often brings one or more companions to share these adventures. His companions are usually humans, as he has found a fascination with planet Earth. He often finds events that pique his curiosity as he tries to prevent evil forces from harming innocent people or changing history, using only his ingenuity and minimal resources, such as his versatile sonic screwdriver. As a Time Lord, the Doctor has the ability to regenerate when his body is mortally damaged, taking on a new appearance and personality. The Doctor has gained numerous reoccurring enemies during his travels, including the Daleks, the Cybermen, and the Master, another renegade Time Lord. Question: What does Doctor Who do when his body is mortally damaged?
regenerate

Passage: In contrast, during wake periods differentiated effector cells, such as cytotoxic natural killer cells and CTLs (cytotoxic T lymphocytes), peak in order to elicit an effective response against any intruding pathogens. As well during awake active times, anti-inflammatory molecules, such as cortisol and catecholamines, peak. There are two theories as to why the pro-inflammatory state is reserved for sleep time. First, inflammation would cause serious cognitive and physical impairments if it were to occur during wake times. Second, inflammation may occur during sleep times due to the presence of melatonin. Inflammation causes a great deal of oxidative stress and the presence of melatonin during sleep times could actively counteract free radical production during this time. Question: Melatonin during sleep can actively counteract the production of what?
free radical production

Passage: Published at a time of rising demand for German-language publications, Luther's version quickly became a popular and influential Bible translation. As such, it made a significant contribution to the evolution of the German language and literature. Furnished with notes and prefaces by Luther, and with woodcuts by Lucas Cranach that contained anti-papal imagery, it played a major role in the spread of Luther's doctrine throughout Germany. The Luther Bible influenced other vernacular translations, such as William Tyndale's English Bible (1525 forward), a precursor of the King James Bible. Question: What work of Luther's became popular?
Bible