30. The flight scheduledat 9 a. m. was delayed four hours due to the bad weather.
A. to take off
B. take off
C. taking off
D. to be taken off
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21. After theythe first super computers in the 1940s, scientists and engineers began to develop ways to create networks.
A. create
B. created
C. have created
D. has created
22. Harvey finished his research paper, but he needed to check it before submitting it to the professor.
A. to type
B. typed
C. typing
D. type
23. We will inform you of the result the program is approved by the board.
A. in order that
B. as if
C. even though
D. as soon as
24. Having your smartphone or computer_ may cause a lot of trouble to you.
A. damaged
B. damage
C. damaging
D. to damage