16.I promise I'll remember ______ the book to you.
A.return
B.to return
C.returning
D.returned
17.They _______ several extra bus lines during the rush hours.
A.get
B.have
C.run
D.take
18.Julia _____ a pleasant hour talking with friends.
A.spent
B.took
C.went
D.cost
19.They succeeded _____ overcoming the difficulties they encountered.
A.to
B.on
C.in
D.of
20.I'll not go to the party _______ I am invited.
A.or
B.till
C.unless
D.when