PTE考生目前最大的问题之一就是练习题缺乏。除了有限的基本官方书（PLUS，Testbuilder, OG）之外,就没有题了。很多英语基础不是很扎实的同学很难找到练习材料。墨尔本文波雅思PTE培训学校专门为墨尔本，悉尼PTE考生准备了适合PTE听力阅读练习的科学60秒。各位PTE同学可以练习PTE听力中的summarise spoken text和PTE口语中的retell lecture，PTE听力口语-科学60秒-Frosty Moss练习记笔记技巧和复述。废话少说，下面开始：
Standard Kilogram Needs Trimming
60秒科学节目（SSS）是科学美国人网站的一套广播栏目，英文名称：Scientific American – 60 Second Science,节目内容以科学报道为主，节目仅一分钟的时间，主要对当今的科学技术新发展作以简明、通俗的介绍，对于科学的发展如何影响人们的生活环境、健康状况及科学技术，提供了大量简明易懂的阐释。
Contaminants have made the standard kilogram weigh slightly more than it originally did, but a careful cleaning method may slim it down. Sophie Bushwick reports
How do you define one kilogram? Easy: it’s the exact mass of a metal cylinder called the International Prototype Kilogram, IPK for short, kept in controlled conditions in France. But the standard kilogram has gained weight since its creation in 1875. To trim it and its many replicas down to size, we need to clean them. The report is in the journal Metrologia. [Peter Cumpson and Naoko Sano, Stability of reference masses V: UV/ozone treatment of gold and platinum surfaces]
When scientists analyzed the surface of an IPK replica, they found it carried tens of additional micrograms. These changes are due to contaminants building up on the kilograms, despite their careful storage under glass. The additional mass is equal to just a few grains of sand. But the kilogram is such an essential unit that tiny changes to different replicas are important.
To remove the contaminants, we need a standard and reproducible cleaning method. Researchers exposed one kilogram measure to ozone and ultraviolet light, which removed the carbon-based contamination without damaging the metal. But to permanently standardize the kilogram, we’ll need to define it in terms of fundamental constants, not a lump of metal in a jar.