Security is a difficult but necessary proposition for any application.
对于任何应用程序，安全是一个困难但必要的命题。
It is a very difficult tip to follow, but a necessary one, if you want to really get out of debt.
这条建议很难做，但又很必要，如果你是真的想要摆脱债款。
Expressing sympathy is a necessary but difficult skill.
表达同情是十分必要而又有难度的技能。
Expressing sympathy is a necessary but difficult skill.
表达同情是十分必要而又有难度的技能。
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