complex problem

Yet, perplexingly, in many cases, imposing sanctions is perceived to be sufficient to address a complex problem.

Climate change is a complex problem, but the required solution is clear.

That has left the White House with a complex problem of communications.

This is ultimately a complex problem in psychology, but it is absurd to pretend that it is an insoluble one.

The grave, complex problem that had baffled his superiors had suddenly simplified itself.

For some years I have been making as scientific and detailed a study as possible of this extremely complex problem.

He was now deeply absorbed in the complex problem 276 of directing and managing his raft.

Did he for instance deal with a succession of simple problems or with one complex problem?