11.   The main problem for the climbers was lack of sleep.

12.   The main problem here is what to do with the existential quantifier.

13.   The main problem in Chechnya today is how to find artificial limbs for amputees.

14.   The main problem in economic terms is that net farm incomes are substantially lower than for other farm enterprises and types.

15.   The main problem is coping with the aggression.

16.   The main problem is energy density.

17.   The main problem is how to be your own critic.

18.   The main problem is the dead hand of local authorities, which keep tens of thousands of properties empty.

19.   The main problem is understood to be integrating the software and the microchip Decoder apparatus in the receiver.