She says the only work needed once beets have been thinned is weeding and, when the weather is dry, a weekly watering.

VOA: special.2010.03.02

So, our bodies are capable of making antibodies that are tuned for all the potential antigens that we come into contact with, That's amazing that we have this capacity to respond and you respond only when needed.

所以 我们的身体具有制造抗体的能力,这些抗体对于各种潜在抗原具有特异性,我们具有只在需要时做出,免疫反应的能力 这太让人惊叹了

耶鲁公开课 - 生物医学工程探索课程节选

Verrocchio told his students that they needed to understand the body's bones and muscles when drawing people.

VOA: special.2010.09.15

Water is needed for cooling the body on hot days, and when we are working or exercising.

VOA: special.2010.07.27

The president also says he will send the military into battle only when needed, and will give them the necessary training and equipment.

VOA: standard.2009.05.23

"We found that easier access to emergency contraception did help women use the pills more quickly when it was needed, and they used it more often, but despite that increased use and faster use, it didn't reduce rates of unintended pregnancy."

VOA: standard.2010.03.22