Know (something) inside out

Do you know the English expression “to know (something) inside out“? Read the conversation below. Can you guess the meaning?

Fatima: I need help marketing my business.

Dennis: You should ask Lisa. She studied it at university. She knows marketing inside out.

Does it mean:

a) have secret knowledge of something

b) have detailed knowledge of something

c) only know the theory of something

d) know the history of something

The answer is below! ↓

business charts commerce computer

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Answer: b) have detailed knowledge of something