31. But , in practice , this could be difficult to enforce . 32. At the camp , it was difficult to see anything . 33. And it's very difficult for them to do those things. 34. This makes the control of chemical pollutants very difficult . 35. That pays tribute to how difficult it was 36. It makes our recognition of our equal humanity difficult. 37. It is extremely easy and it is very difficult 38. ” I can interpret it , but the interpretation is very difficult . 39. They learn to spell more difficult words . 40. It is , however , quite difficult to answer this question .
