Infancy is a uniquely vulnerable period of rapid growth and development.

婴幼儿处于生长发育极其迅速的关键时期。

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The transition from exclusive breastfeeding to full use of family foods is a very vulnerable period.

从完全母乳喂养到充分利用家庭食物的过渡是一个非常脆弱的时期。

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Complementary feeding typically covers the period from six to 24 months of age, and is a very vulnerable period.

补充喂养通常涵盖了6至24个月龄这一年龄段，这是一个非常脆弱的时期。

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Those unvaccinated children are now entering a vulnerable period in their lives as they move to secondary school.

BBC: Children in Devon and Cornwall urged to have MMR jab

Will BAE be vulnerable in that period to an opportunistic bid from one of its US rivals, such as Lockheed?

BBC: How Germany killed the merger of BAE and EADS

For example, online retailers are especially vulnerable during the peak shopping period between Thanksgiving and Christmas and especially on Cyber Monday.

FORBES: Figuring DDoS Attack Risks Into IT Security Budgets