Many students purchase used books from the bookstore. Used books are cheap. My parents didn t want me to buy a new car. I bought a new car in 1997. The second sentences are less important to the reader s understanding than the first in these cases.
Many students purchase used books from the bookstore because used books are cheap .
My parents opposed my purchase of a new car in 1997 . Subordination makes the new sentences clear and pleasing to the reader. Always use a comma after an introductory subordinate clause.