One effective technique for proofreading your work is to
a. read the writing of another author.
b. read what you have written, backward.
c. turn off computer spell-check programs.
d. substitute words that you know for words that you don't.

The correct answer is: turn off computer spell-check programs. 

Sometimes, computer spell-check programs could be a little confusing. One effective technique for proofreading your work is to turn it off, read your work again so that you'll be able to spot mistakes for yourself. 

So kristen decided to call a taxi. “so” is a subordinating conjunction.