Here are the best options for each blank from the passage you provided:

1. C. Whenever
2. A. Since
3. B. as
4. C. although
5. C. in spite of
6. B. in order to
7. C. although
8. B. in order to
9. C. so that
10. A. because
11. B. until
12. C. be
13. C. until
14. A. unless
15. B. Since
16. D. Although
17. B. Although
18. C. though
19. A. because
20. D. but
21. A. if
22. C. because
23. B. and C are correct
24. C. Thus
25. A. and B are correct
26. C. whereas
27. B. because
28. D. although
29. C. as
30. B. when
31. C. because
32. A. Although
33. D. Despite
34. B. when
35. C. so
36. D. as
37. C. unless
38. A. Although
39. C. because
40. B. unless
41. D. despite
42. A. as
43. C. when
44. B. so
45. D. because
46. C. before
47. B. had
48. A. because
49. D. where
50. B. unless

Feel free to ask if you have more questions!