It is necessary initially to classify the headaches into certain types.

起初把头疼分成若干类别是有必要的。

《柯林斯英汉双解大词典》

There will still be lots of challenges if we are to classify garbage in a short time.

如果我们要在短时间内对垃圾进行分类，仍然会有很多挑战。

youdao

Thing is that it's very difficult to classify.

问题是很难进行分类。

youdao

There's the weird diets but hard to classify: Detox Diet, The Rave Diet, so if you're into raves you can go do that, and The Negative Calorie Diet, so these -the Negative Calorie Diet are ones that- where you eat food that have negative calories, so you consume it but it burns off more calories than it actually has.

这些是难以归类的减肥法,排毒法,锐舞减肥法,如果你对锐舞感兴趣,就可以照着做,还有负热量减肥法,负热量减肥法是指,吃具有负热量效应的食物,当你吃它的时候,消耗掉的热量比食物本身所含热量还多

耶鲁公开课 - 关于食物的心理学、生物学和政治学课程节选

Thing is, it's very difficult to classify,

重要的是，它难以分类，

街头时尚的精髓 - SpeakingMax英语口语达人

So let's think about how we can classify single and double and triple bonds, which is what we're really used to dealing with in terms of these sigma bonds and these pi bonds.

让我们想想怎么来分类单键双键,和三键，这在我们在考虑sigma键,和π键是很有用的。

麻省理工公开课 - 化学原理课程节选

All were Americans, but they were asked to classify themselves by race as well.

ECONOMIST: The genetics of happiness

Further, it is an unbelievable basis on which to classify them as conscientious objectors.

CENTERFORSECURITYPOLICY: Center For Security Policy

Let me first define the word optimism and what it means to classify oneself as an optimist.

FORBES: Why Communicators Must Be Optimists