Delighted as I am to be the new mother of twins, I find raising multiples extremely challenging.

There is also a lot of obstacles to make the course extremely challenging for anyone.

The pilots found the flying extremely challenging for a number of reasons.

However, due to its passage through congested and built-up parts of town, it would be extremely challenging to widen the route.

The shells of species within this family vary greatly and can sometimes be extremely challenging to identify.

The human brain has approximately 100 billion neurons connected through complex networks, making it extremely challenging to trace the brain's wiring plan.

These ongoing problems make forecasting exchange rate movements extremely challenging.

Whatever the excuse, this is a pretty impressive summit meeting of jazz saxophone talent: learned, sweepingly comprehensive, extremely challenging at their best.

Moreover, bitter partisanship has made it extremely challenging to pass legislation.

The way atop the hill is pretty exciting up to some 1 km and extremely challenging to go beyond that.