SUPPOSED TO: correct form for “to be obligated to” or “presumed to”
Example: Grandma’s plane is supposed to arrive at 10:30.
SUPPOSE: to guess or make a conjecture
Example: Julie supposes Grandma’s plane will be on time.
THAN: use with comparisons
Example: Many soldiers would rather make dinner in a Crock-Pot than eat at the DFAC.
THEN: at that time, or next
Example: I ate dinner at home, and then I went out for dessert.
THROUGH: by means of; finished; into or out of
Example: The car crashed through the wooden fence.
THREW: past tense of throw
Example: She threw away the leftover food.
THRU-abbreviated slang for through; not appropriate in standard writing
Example: Bob and Fed are thru with work for the day and will grab dinner at the drive-thru.
WHO: (pronoun) refers to a person(s)
Example: Jenna wondered why Jack, who was always punctual, was late picking her up.
WHICH: (pronoun) replaces a thing(s)s
Example: Which book genre is your favorite?
THAT: used to refer to things or a group or class of people
Example: Miranda lost the book that she borrowed from the library.
WHO: used as a subject or as a subject complement
Example: Steve is the man who will get the job done right.
WHOM: used as an object
Example: Whom did Sarah choose to go with her?