1. Usage Review D

2. of
Of is a preposition. Do not use in place of have after verbs such as could, should, would, might, must, and ought to.
Incorrect: You should of studied more for the test.
Correct: You should have studied more for the test.

3. Raise, rise
Raise means "to make higher," "build," or "nurture and cause to grow." It is normally transitive, that is, the action is done to something or someone else.
Correct: They raised the barn in two days.
Rise means "to get up" or "become elevated." It is never transitive. The past tense is rose; the past participle, risen.
Correct: The sun rises and sets every day.

4. sit, set
Set means to "put in a certain place." It is normally followed by a direct object, that is, it acts upon something else. It is transitive.
Sit means "to be seated." It is always intransitive.
Incorrect: Set down on this chair.
Correct: Sit down on this chair.
Incorrect: Sit the money on the counter.
Correct: Set the money on the counter.

5. than, then
“Than” is the word you want when doing comparisons. But if you are talking about time, choose “then.”
Incorrect: Alexis is more skilled at the piano then I.
Correct: Alexis is more skilled at the piano than I.

6. their, there, they’re
Their is a possessive pronoun. It always describes a noun.
Note the spelling of their. It comes from the word they, so the e comes before the i.
There is an adverb meaning "that location." It is sometimes used with the verb to be as an idiom. It is spelled like here which means "this location."
They're is a contraction of they are. Note the spelling: The a from are is replaced by an apostrophe.

7. their, there, they’re Examples:
Their dog has fleas. (possessive of they)
I put the collar right there. (that location)
There are five prime numbers less than ten. (with to be)
They're 1, 2, 3, 5, and 7. (contraction of they are)

8. theirs, there’s Theirs is a possessive pronoun.
There's is a contraction for there is or, rarely, there has. Note the apostrophe replacing the missing letter or letters.
Their's does not exist.

9. their, there, they’re Examples: That painting is theirs.
(possessive pronoun)
There's more to this than meets the eye.
(contraction of there is)

10. who, which that
Who (and its inflections, whom and whose) is used to refer only to people or to entities treated as people (e.g., gods, or anthropomorphized pets).
That is used to refer to animals, things, or people. Although as a general rule who is preferred for people, that is also acceptable for referring to people when the relative clause is restrictive, and sometimes using that will make the sentence read better.

11. who, which that
This is the boy who stole money from an old man who had gone out of his way to help him.
This is the boy that stole money from an old man that had gone out of his way to help him.
This is the boy that stole money from an old man who had gone out of his way to help him.
This is the boy who stole money from an old man that had gone out of his way to help him.
 Although all of four these sentences are "correct," the last two examples read better than the first two, because they avoid awkward repetitions.

12. who, which that
Which is used to refer to things or animals, not people. When the clause is nonrestrictive, use who, not which to refer to people.
Examples:
The books, which are on the table, are antiques.
The students, who are waiting patiently, are ready to leave for the summer.

13. who’s, whose
“Who’s” always and forever means only “who is,” as in “Who’s that guy with the droopy mustache?” or “who has,” as in “Who’s been eating my porridge?” “Whose” is the possessive form of “who” and is used as follows: “Whose dirty socks are these on the breakfast table?”

14. your, you’re
You're is the contracted form of You are. This form is used in sentences using "you" as the subject of the sentence with the verb "to be" used as either the helping verb (e.g. You're going ..., You're watching ...) or the principal verb of the sentence. Your is the possessive pronoun form. This form is used to express that something belongs to "you".