* "Glad to hear it" is correct and commonly used when responding to good news.
* "Glad to hear this" is also correct, but slightly less common than "Glad to hear it."
* "Glad to hear that" is also correct and a bit more formal than "Glad to hear it."
The issue with "that" is that it's redundant. "Glad to hear" already implies the speaker is happy about something you just mentioned.
So, to answer your question about native English speakers, here are the best options:
"Glad to hear it" - This is the most natural and casual option.
"Glad to hear this" - This is also correct, but a bit less common.
"Glad to hear that" - This is the most formal option.
Example:
You: "I got a promotion at work!"
Friend: "Glad to hear it!"
Let me know if you have any other questions about English grammar!