The correct meaning for the idiom "Take with a grain of salt" is B: Doubt something. This idiom suggests that you should not believe something completely or literally, but rather view it with a degree of skepticism or caution. It implies that the information might not be entirely accurate, reliable, or true, and therefore, you should not accept it at face value.
The origin of this phrase is often attributed to ancient Roman scholar Pliny the Elder, who, in his "Naturalis Historia," mentioned an antidote for poison that included a grain of salt. The idea was that the salt made the antidote more effective or palatable, metaphorically making a piece of information easier to swallow if you approach it with a bit of skepticism. Over time, it evolved to mean that one should be cautious and not fully believe something.
For example, if someone tells you a wild story, you might say, "I'll take that with a grain of salt," meaning you're not entirely convinced.