An attack rate is an incidence rate usually expressed as a percentage.

发病率是将疾病发生率用百分数表示。

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Design is at least partly about resolving competing requirements, usually expressed as forces.

设计工作至少有一部分需要考虑如何解决存在冲突的各个需求，这些需求通常表述为影响因素 (force)。

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They are usually expressed as declarative statements in the form of "the system shall do..."

它们通常被表示为“系统应做…”形式的陈述语句。

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Each dollar of income is taxed at 40.788% (usually expressed as the rounded amount of 40.8%).

FORBES: Impact of the "Fiscal Cliff" Tax Legislation on Charitable Giving in 2013