Sure! Here’s a rewritten version for each sentence:

31. I couldn't take the test due to its difficulty.
- I couldn't take the test because of...

32. He studies hard, despite facing difficulties.
- Despite...

33. Since I don’t know Russian, I needed the document translated into French.
- Because...

34. They continued to work even though it got dark.
- In spite of...

35. He has an English name; however, he is actually German.
- Despite...

36. These students arrived late due to having an accident.
- Because...

37. Nick is frequently punished for being lazy.
- Because of...

38. We bought the house even though the rooms were small.
- We bought the house despite...

39. The accident occurred because he was negligent while driving.
- Because...

40. Karen works on Sundays to earn extra pay.
- Because of...

41. Even though he planned everything carefully, many things went wrong.
- Despite...

42. She ate much due to her hunger.
- Because...

43. Even though the prices are high, my daughters still want to see the movie.
- Despite...

44. We didn’t go fishing because the water conditions were rough.
- Because of...

45. They study hard, yet they still can’t achieve good marks.
- In spite of...