21. John failed _____.
A. because he did not study hard
B. since he stopped to study hard
C. due to study hard
D. because of he did not study hard
22. I ordered two pizzas _____ we were all hungry.
A. when B. while C. as D. soon
23. The conference had to be cancelled _____ a key piece of equipment was out of work.
A. since the fact B. because of
C. as the fact D. due to the fact that
24. The expedition had to be postponed _____ there was a typhoon.
A. so as to B. with a view to
C. as long as D. on account of the fact that
25. Tony had little difficulty in passing the examination, _____ he has a very good foundation in English.
A. since B. as C. for D. because