For two or three generations past, ever- increasing numbers of individuals have been living as workers merely, not as human beings. An excessive amount of labour is rule today in every circle of society, with the result that man's spiritual element cannot thrive. He finds it very difficult to spend his little leisure in serious activities. He does not want to think; or he cannot even if he wants to. He seeks not self- improvement, but entertainment which would enable him to be mentally idle and to forget his usual activities. Therefore, the so- called culture of our age is dependant more on cinema than on theatre, more on newspapers, magazines and crime stories than on serious literature. The passage is based on the idea that,

The passage primarily discusses how "an excessive amount of labour" leads to people living as mere workers, preventing their spiritual element from thriving, making serious activities difficult, and driving them towards idle entertainment. This "excessive amount of labour" directly translates to "overstrain."

Analysis of options: A) man should not work hard: The passage criticizes "excessive" labour, not hard work itself. This option is an overgeneralization. B) the great evil of our age is overstrain: This option perfectly captures the central theme. The passage repeatedly points to "excessive amount of labour" as the root cause of all the described problems, which is synonymous with overstrain. All the negative consequences (inability to think, seeking entertainment, decline of serious culture, spiritual stagnation) stem from this overstrain. C) man cannot think well: This is presented as a consequence of the excessive labour and overstrain, not the fundamental idea the passage is based on. D) man cannot care for his spiritual welfare: This is also a result of the excessive labour and overstrain ("man's spiritual element cannot thrive"), rather than the core idea or the "great evil" itself.

Therefore, B is the most accurate summary of the passage's underlying idea.