在先

I had collected material previous to writing.

我在写作以前先搜集了材料。

Sugar, oil and metals are refined before use.

糖, 油和金属在使用前须先提炼。

Filter out all the dirt before using the water.

在用水以前先将清洁的东西过滤掉。

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

挑选受者在同一时段先行前测，行后测，测完毕后行比较分析。