effective 
英 [ɪˈfɛktɪv]  美 [ɪ'fɛktɪv] 
adj. 有效的；生效的，起作用的；有力的；实际的

例句：
What is the most effective way of teaching children to read and write? 

用什么方法教孩子阅读与写作最有效？

The vaccine is effective against the most common strain of the disease. 

疫苗可以有效防范这种最常见的疾病。

an effective public transport system 

有效运转的公共交通系统

He assumed effective command of the armed forces. 

他实际担任起了武装部队的指挥。

The rebels have been in effective control of the island since March. 

反叛分子自3月起就已实际控制了该岛。