So all drugs must have a specific chemical composition which gives them the key to unlock this barrier and pass through.

因此， 所有药物都必须具有特定的化学成分，这为它们提供了打开此屏障并通过的钥匙。

After a particularly violent storm, scientists identified dust from the Sahara Desert thousands of miles away in London, based on its specific composition.

在一场特别猛烈的风暴过后，科学家们根据其特定成分，确定了来自数千英里外伦敦撒哈拉沙漠的灰尘。