11.It was not yet eleven o'clock _____ a boat crossed the river with a single passenger who had obtained his transportation at that unusual hour by promising an extra fare.
A.what
B.when
C.that
D.which
12.Women workers wear hats _____ their hair gets caught in the machinery.
A.if
B.in case
C.unless
D.because
13.No sooner had they come back _____ they went to sleep.
A.when
B.then
C.until
D.than
14.It _____ our teacher came that we begun the test.
A.was until
B.was not until
C.not until
D.until was
15._____, glasses can correct most sight defects in healthy eyes.
A.When well fitted
B.Being fitted
C.was fitted
D.fitted
16.We should make a clear _____ between the two scientific terms for the purpose of our discussion.
A.distinction
B.discrimination
C.deviation
D.separation
17.Rumors are everywhere, spreading fear, damaging reputations, and turning calm situations into ______ ones.
A.tragic
B.turbulent
C.vulnerable
D.suspicious
18.I was deeply impressed by the hostess' ________ and enjoyed the dinner party very much.
A.hostility
B.indignation
C.hospitality
D.humanity
19.All imaginative _______ is a reflection of the real word.
A.invention
B.creation
C.discovery
D.illusion
20.Two discussions from different points of view may ______ each other.
A.complexion
B.compliment
C.appendix
D.complement