I can hardly imagine Peter's _____ across the Atlantic Ocean in five days.
A. sail
B. to sail
C. sailing
D. to have sailed
_______, they will go and visit the zoo.
A. Weather permitting
B. Weather permitted
C. Weather being permitted
D. Weather having permitted
Having been attacked by terrorists,______.
A. doctors came in their rescue
B. the tall building collapsed
C. an emergency measure was taken
D. warnings were given to tourists
While watching TV,____.
A. the door bell rang
B. the door bell rings
C. we heard the door bell ring
D. we heard the doorbell rings
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