在先

I had collected material previous to writing.

作以前先搜集了材料。

Sugar, oil and metals are refined before use.

糖, 油和金属使用前须先提炼。

Filter out all the dirt before using the water.

用水以前先将其中不清洁的东西过滤掉。

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

挑选受者同一时段先进行前测卷，再进行后测卷，测完毕后再进行比较分析。