11.   The added price of inconvenience is hard to measure and must be inferred from indirect evidence.

12.   The men were so tired they found it hard to March.

13.   The relative importance of habit and biological factors in such circumstances is hard to Decide.

14.   The true effect on wild dolphin populations of prolonged exposure to chemical pollutants is hard to measure.

15.   To what extent this promotes economic power would be hard to estimate, but the two are certainly not unrelated.

16.   Viewed head-on from short range the animal is exceedingly hard to spot, provided it stands still.

17.   We found his statement hard to credit.

18.   Whether such pragmatism will continue to thrive among home users is hard to judge.

19.   Many employers find it hard to delegate.

20.   English grammar can be hard to master.