complicated  adj. 复杂的

= sophisticated 

= intricate = complex

approach  n. 方法

= method = means

adopt  v. 采取

adapt to 适应

obtain  v. 获得

= gain = acquire

combat  v. 与…战斗

crucial adj. 重要的

= vital = important

A complicated approach was adopted, which made use of quinine – a drug obtained from tree bark which had long been used to combat fever, but was now seen as a crucial part of the war on malaria.

语法点：句子主干：a complicated approach was adopted… but was now seen as…

理解：利用奎宁物质预防疾病的一种复杂方法被采纳，此物质从树皮中获得并很长一段时间用于抵抗患热病，但是现在对预防疟疾至关重要。