1. Pages 259-260,
Exercise 23
Decide which of the of the following
sentences contains a nonessential
adjective clause. Put commas in those
sentences. If the sentence doesn’t
need commas, write NC.

2. 1. Kids who spend
a lot of time on
the computer
don’t get much
exercise. NC

3. 2. My grammar
teacher, who has
been teaching here
for twenty years,
knows a lot about
computers.

4. 3. Freecycle,
which was
created in 2003,
helps keep things
out of landfills.

5. 4. People who get
spam every day
can get very
annoyed. NC

6. 5. My best friend,
who gets at least 30
pieces of spam a
day, wrote a letter
to his senator to
complain.

7. 6. Berners-Lee,
whose parents were
very educated,
loves learning new
things.

8. 7. Meg Whitman,
who ran eBay for
ten years, decided
to run for governor
of California.

9. 8. Berners-Lee
worked in
Switzerland, where
the CERN physics
laboratory is located.

10. 9. The Windows
operating system,
which was developed
by Microsoft, came out
in 1985.

11. 10. Did you like the
story that we read
about Berners-Lee? NC

12. 11. The computer (that)
you bought three years
ago doesn’t have enough
memory. NC

13. 12. The computer (=
computers), which is one
of the most important
inventions of the
twentieth century, has
changed the way people
process information.

14. Special problem when you talk
about a general class of
things.
For example, “The computer
was invented in the 20th
century.”
In English, there are two ways
to talk about a general class of
things:

15. “The computer” can mean
“computers,” or “all computers.”
The computer was invented in the
20th century = Computers were
invented in the 20th century.
The tiger is almost extinct =
Tigers are almost extinct

16. When you use an adjective
clause after a general class
of things, it has to be non-
essential, and it needs
commas:

17. The computer, which was invented in
the 20th century, has changed the
way people process information =
Computers, which were invented in
the 20th century, have changed the
way people process information.

18. The tiger, which is prized in Asia as a
source of medicine, has been hunted
almost to extinction =
Tigers, which are prized in Asia as a
source of medicine, have been
hunted almost to extinction.

19. 13. Bill Gates, who
created Microsoft with
his friend, became a
millionaire.

20. 14. My best friend,
whose name is on my
buddy list, contacts me
every day through an
instant message.