relate to 和 relative to 和 relevant to 的差別在哪裡？如果不好說明，請提供一些例句。

To relate to means that something can understand the feelings of something else.
"I can definitely relate to you."
It can also mean that two things have a logical connection
"This book relates to the author's thoughts about life."

"Relative to" means that something is measured from something else.
"A sandwich is huge, relative to an ant"
"Relative to his, your life is unimportant."

"Relevant to" means that something has an important meaning for something else.
"Their speeches are relevant to our lives."
"This book is relevant to my experience."

You can use the last two as adjectives, too:
"The relative speed is 12 miles per hour" (the speed is relative to something else)
"That's the most relevant thing I've heard all night" (the thing is the most relevant to something)