简述浪漫主义时期音乐的旋律。
参考答案：
旋律优美，富有激情，抒情性大大加强，乐句结构的伸缩性也很大，在民族音乐中旋律带有民间特色。
Why didn’t you tell me about your trouble last week? If you（）me, I could have helped.
A. told
B. had told
C. were to tell
D. would tell
一般一个操作系统要提供三类接口给不同类型的使用者，是哪三类接口
