n.有效性；效力
I doubt the effectiveness of the medicine. 我怀疑这种药的有效性。
Once a contract is signed, it has legal effect. 合同一旦签署即具有法律效力。
When I was sad, music had a therapeutic effect. 我悲伤的时候,音乐有治疗效力。
n.低效率；无效
