He says a less costly, easy-to-use medicine for sleeping sickness is badly needed.

VOA: special.2010.04.07

The "When" pattern is very easy to use.

When”句型使用起来非常方便。

When 课堂 - SpeakingMax英语口语达人

He says an cheap and easy-to-use medicine for sleeping sickness is badly needed.

VOA: standard.2010.04.05