Student or Learner
A: You have three pens. Haven't you?
B: Yes, if you want, you can take one of them.
Is the usage of "them" correct here? I thought them can only be used when what we are referring to is human beings or living things. What is the difference if we use those instead of them here?
"those" is also correct, although I agree that "them" would be used more often in the phrase you have highlighted.
Both "them" and "those" may refer to both animate and inanimate [living and non-living] objects.