The conjectures of the Langlands program are a challenge to the next generation of mathematicians.

解释：形体弯曲，影子自然就曲；形体正直，影子自然就正。

The metropolis exacts from man as a discriminating creature a different amount of consciousness than does rural life.

The balance between economic growth and environmental responsibility is the defining challenge of our time.

"The power of literature lies in its ability to make us see the world differently."