今天我们要学的词是 effective. Effective 有效的。The U.S. Center for Disease Control and Prevention says this year's flu shot is less effective because the current flu virus has mutated. 美国疾病预防和控制中心说，由于流感病毒变异，今年流感疫苗的防疫效果可能不是很有效。Indonesia has developed a male birth control pill that is 99% effective. 印度尼西亚开发出了一种男用避孕药，有效率高达99%。好的，今天我们学习的词是 effective, effective, effective...
