合奏时，各种乐器一起敲击，交相呼应，起伏跌宕。
At the other rime of ensemble , all the instruments are played together echoing each other .
双相障碍是以起伏性躁狂或抑郁为特征的慢性周期性精神疾病。
Bipolar disorder is a chronic and recurrent psychiatric disorder , which is characterized by waving mania or depression .
相起伏