They contain nitrogen and usually occur as salts of asids such as citric, malic, and succinic acids such as citric, malic, and succinic acids.是什么意思_They contain nitrogen and usually occur as salts of asids such as citric, malic, and succinic acids such as citric, malic, and succinic acids.在線(xiàn)翻譯_英語(yǔ)_讀音_用法_例句