We still can’t figure out how to make hydrogen fuel cells efficient, safe and practical and hybrids/deisal cars are yesterday’s news.

我们仍无法找出让氢燃料电池高效、安全、实用的方法，而混合动力车已是昨日之旧闻。

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Some classes retain state information from one method invocation to the next, and it is difficult to make such classes thread-safe in any practical way.

有些类保留从一个方法调用到下一个方法调用的状态信息，要在实践中使这样的类成为线程安全的是困难的。

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Many workers across the public and private sector do very physically demanding jobs where carrying on until 66 is not a safe or practical option.

许多人在公共部门和私人企业从事的是体力损耗很大的工作，在这样的岗位工工作到66岁并不安全或者可行。

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The concept of burning away tumors with electric current dates back a century, but it took modern imaging machines to make through-the-needle tumor-burning accurate enough to be safe and practical.

FORBES: Magazine Article

Boasting an aluminum base, the Wooden Light Bulb is totally safe (although probably not that practical for actual lighting purposes) as LEDs, unlike incandescents, produce a very small amount of heat.

FORBES: Designer Unveils Wooden Light Bulb

But it's just not practical, it's not possible, it's not safe for them to do that.

BBC: Obesity rates fall in Philadelphia