Hi Dinghui! The difference between "Do you know?" and "Did you know?" lies in their tense and usage: 1. Do you know? This phrase is in the present simple tense. It is typically used to inquire about someone's current knowledge or understanding of a particular fact, topic, or situation. It is a general question that does not imply any specific time frame. For example: "Do you know where the library is?" "Do you know how to speak Spanish?" 2. Did you know? This phrase is in the past simple tense. It is used to ask if someone was already aware of a particular fact or information, usually with the implication that the information is surprising or new to the listener. It often introduces interesting or unexpected information. For example: "Did you know that the Earth is round?" "Did you know that elephants can communicate over long distances using infrasound?" Hope it helps! :)

I mean in this context, apparently “I wouldn’t know” before I read the “following paragraph”.

‘Did you know…?’ indicates that I already know. It’s not really looking for an answer. It’s kind of like saying ‘Here’s an interesting fact.’ ‘Do you know …?’ could mean, but doesn’t necessarily mean, that I don’t know myself, and could be looking for an answer. I’m not sure why! Great question.

In this context, you can use them interchangeably.

"Did you know this?" is similar to "do you already know this?"