Litmus paper can be used as an indicator of the presence of acid in a solution.
石蕊试纸可用以测试溶液是否含酸.
The analysis showed a few grains of arsenic in the solution.
分析显示溶液中有几格令的砷.
We haven't found the solution yet, but I'm sure we're on the right track.
我们还没有找到解决办法, 但我肯定我们的思路是对的.