Quote Originally Posted by HSS View Post
One more thing, Raymott.

By the same token, are the following then are not correct, either?
3 Tira is going to give Hiro a pencil, which she bought at the store last week.
4 Tira is going to give Hiro pencils, which she bought at the store last week.

Your help would be very much appreciated.
They are correct if you're adding additional information about the pencils that doesn't say which pencils you mean.
If you using the clause to define which pencils, the comma is wrong, and you need, "Tira is going to give Hiro the pencils which she bought at the store last week.
Which pencils? - The pencils which she bought at the store. (No comma)
You can look here (and elsewhere):
Clauses - Restrictive and Nonrestrictive