She had to work deep into the night, she couldn't have spread the messages to all the relevant people successfully.
A. while
B. but
C. otherwise
D. so
网友回答
A. while
B. but
(答案→)C. otherwise
D. so
解析：考查虚拟语气。句义：她不得不工作到深夜，否则的话她就不能成功地把信息传播到相关人员。把握关键词couldn't have spread，对过去的虚拟，根据前面She had to work deep into the night过去的事实，otherwise +过去的虚拟，所以C正确。