sole

The sole effective weapon we have is knowledge.

I think that there is someone whose job it is at Apple, someone whose sole purpose is to come up with one obnoxious thing to complain about for every new Apple product redesign.

This can help us anticipate what will happen in the future, like if a koala population is growing so fast that there won’t be enough of its sole food resource, eucalyptus leaves, to support the population.