Litmus paper turns red in the presence of an acid.

石蕊试纸遇到酸就变红。

《牛津词典》

A lemon is an acid fruit.

柠檬是一种酸味水果。

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These shrubs must have an acid, lime-free soil.

这些灌木必须要有酸性、无石灰的土壤。

《柯林斯英汉双解大词典》

But it is the first time an amino acid has been discovered on a comet.

VOA: special.2009.09.30

And what it's used is to convert one type of group, what's called a carboxylic acid into another type of very reactive intermediate, which is called an acid chloride.

它被用来将一类被称作羧酸的化合物，转化成另外一类活性很高的反应中间体,也就是酰氯。

麻省理工公开课 - 化学原理课程节选

So I show that here, so in green, you have what's called a carboxcylic acid group, a c o o h, which gets converted by s o c l 2 to a c double bond o c l or an acid chloride.

我在这里用绿色表示，我们所说的羧酸族化合物，碳，氧，氧，氢，它被亚硫酰氯转化为,一个碳氧双键与碳氯单键组成的酰氯。

麻省理工公开课 - 化学原理课程节选

It also attacked Streptococcus mutans, an acid-producing bacterium which is a major cause of tooth decay.

BBC: Coconut oil could combat tooth decay

Two people have been arrested on suspicion of involvement in an acid attack on a woman in east London.

BBC: Naomi Oni acid attack: Man and woman arrested

The most commonly used lemon-flavor molecule, citral, fades within 30 days when put in an acid medium like lemonade.

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