While the need to rank historical causes in some order of importance may seem obvious to most historians, such hierarchies raise serious philosophical difficulties.

虽然对大多数历史学家来说，根据重要性对历史原因进行排序的必要性似乎是显而易见的，但这种等级制度引发了严重的哲学难题。

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Yet the fall in the fertility rate may reflect dissatisfactions too: notably, over the difficulties faced by women who want both to work and to raise a family.

但是生育率的下降也反映出一些不满情绪：最显著的是既要工作又要顾家的妇女面临的重重困难。

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But bioprospecting has done almost nothing to raise the value of standing forests. This is partly because of difficulties in attaching property rights to species.

但是生物勘探对现有森林的价值提升几乎没有贡献，部分因为为物种加上产权是比较荒唐的。

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However, it acknowledges that introducing a legal obligation for companies to make payoffs proportionate to performance would raise practical difficulties, as directors often step down for reasons unconnected with the fortunes of the company.

BBC: 'Fat cat' pay proposals: At a glance

Instead they argue that there should be a substantial pay rise for all teachers which will raise morale and help to tackle the difficulties in recruiting new teachers.

BBC: Performance pay 'doomed to fail'

Companies trying to raise capital for a business plan involving location information can have difficulties as investors see the uncertainty as a liability.

FORBES: Lawmakers Propose Changes To Make Government Get Warrant Before Reading Your Email