Man needs difficulties; they are necessary for health.

人需要困扰，困扰是心理健康的必须之物。

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Man needs difficulties; they are necessary for health.

人需要困扰，困扰是心理健康的必需之物。

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Dutch bacteriologist who inadvertently proved the existence of a dietary factor (a vitamin) necessary for health.

荷兰细菌学家，不经意间证明了一种食物因子(维生素)对身体健康的重要性。

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Some good bacteria are absolutely necessary for overall health and not just bowel health.

CNN: Could I become dependent on probiotics?

In Europe, some politicians like to say growth is necessary to pay for health care and other goodies.

ECONOMIST: Asian welfare states

Based on a thorough review of the available scientific information, FDA has created a strategy for the judicious use of medically important antimicrobials in food-producing animals that states their use should be limited to situations where the drugs are necessary for ensuring animal health, and done so under veterinary guidance.

FORBES: Are You Eating 'Superbugs'? The FDA Responds To Allegations Of Antibiotic Resistance On Meat