These four pronouns are also troublesome. Sometimes when they are used in sentences,
their reference is unclear.
I bought a watch, pen,
and cell phone. It cost fifty dollars.
What cost fifty
dollars? We do not know.
I bought a watch, pen,
and cell phone, and the phone cost fifty dollars.
The CD and the book
are best sellers, but this is better.
What is better?
We are not sure.
The CD and the book
are best sellers, but this book is better.
Now, the pronoun this
pulls in the reference book.