Correct Answer: to hear directly from someone who knows

Solution : The most appropriate meaning of the underlined idiom is the second option.

Explanation : The idiom "from the horse's mouth" is used to convey that the information or news comes directly from a reliable and authoritative source. The term likely originated from horse racing, where gamblers would try to get information about a race directly from the trainers or jockeys, who were considered the most knowledgeable sources.

In the context of the sentence, the speaker is emphasising the credibility and reliability of the information by stating that it was heard directly from the source.

Therefore, the correct meaning of the idiom is to hear directly from someone who knows.