Sugar, oil and metals are refined before use.

糖, 油和金属在使用前须先提炼。

I had collected material previous to writing.

我在写作以前先搜集了材料。

The research tools are the vision-eikon-compare test 1 and test 2.

挑选受试者在同一时段先进行前测，再进行后测，测试完毕后再进行比较析。

Filter out all the dirt before using the water.

在用水以前先将其中不清洁的东西过滤掉。