He seldom stays up late at night,_______ he has too much work to do.
连词。
句意：他晚上很少熬夜，除非他有很多的工作要做。unless 意味“除非"，符合题意。
_______ people were found _________ after that earthquake.
句意：在那次地震后一些人被发现死了。前空考查 a number of ...，意为“一些”； 后空考查形容词作主语，故选A。
A number of 与 The number of 的区别。