【题目】He is writing a book about new discoveries in science. I am sure, _________ it is printed, this book will be very popular.
A.once
B.while
C.now that
D.though

【答案】A
【解析】句意：他正在写一本关于科学新发现的书。我确定，一旦这本书被出版，一定会非常受欢迎。A. once一旦；B. while而，虽然，在…期间，与…同时；C. now that既然；D. though尽管。根据句意可知选A。