prep-ds1-20 答案应该没有错的啊？

20.   1491-!-item-!-187;#058&000755
                ?

A certain one-day seminar consisted of a morning session and an afternoon session.  If each of the 128 people attending the seminar attended at least one of the two sessions, how many of the people attended the morning session only?

(1) 3/4 of the people attended both seminars

(2) 7/8 of the people attended the afternoon session.

答案=B？

百思不得其解，上面说的at least那早上的人可能参加下午的，B怎么能够推出上午的呢！Prep答案应该没有错的啊？

attended the morning session only?

发现答案了，这里说了only，所以只需要知道参加下午的……