hard to tackle

However, most of the traditional rule-based classification algorithms use sequential covering technique when training classification rules which has some challenging problems hard to tackle, especially in classification for rare class.

但是，传统的基于规则的分类算法多数采用顺序覆盖技术来训练分类规则，这种方法有着自身无法很好解决的问题，在稀有类分类中这种问题更加突出。

Answer: Keep a kid fee money again hard to tackle, a personal very busy, so demand two personal division of labour.

答：因为养孩子费钱又费力，一个人忙不过来，所以需要两个人分工合作。

Interpolation theorem and preservation theorem in first order logic have determined the existence of first order formula in accordance with certain conditions, their proofs in classical model theory are fairly long and hard to tackle.

一阶逻辑的内插定理和保持定理确定了符合某些条件的公式的存在性，经典模型论中对这些的证明较为繁难。

Without a healthy mentality, it is hard for one to tackle the tierce social competitions which are striking our middle school campus constantly. Thus bringing more challenges to the mental health of the middle school students.

没有良好的心理素质，就很难应对社会的激烈竞争。而这样的竞争正在冲击着我们的中学校园，对中学生的心理素质提出了较高的要求。

Such therapy also opens up the possibility of finding better treatment options for a string of genetically-driven illnesses that have been hard to tackle with traditional medicine, such as cystic fibrosis and Huntington's disease.

这种疗法还使得为一系列由基因导致的疾病找到更好的治疗选择成为可能，这类疾病很难依靠传统药物治疗，例如囊性纤维化和亨廷顿氏病。

Poverty and unemployment are frustratingly hard to tackle.

贫穷和失业是难以解决的问题，这常常让人泄气。