In recent years, security incidents about drugs take place one after another.

近些年来，关于药品的安全事件此起彼伏，不绝于耳。

When the global water crises take place one after another, most African countries have also emerged in the water crisis.

在全球水资源危机此起彼伏的时候，多数非洲国家也出现了水危机。