Threw is the simple past tense of the verb throw. (Buddy threw the ball.)
Through can function as an adjective, adverb, or preposition, each with a variety of meanings. Through often suggests a passage—from start to finish, or from point A to point B. (Buddy walked through the museum.)
Thru is an informal spelling of through--more appropriate in a text message than in a formal essay or report.
- Lena threw me a kiss as she ran out the door.
- She came in through the bathroom window.
- I’ll call you when I’m through [or, in a text message, thru] writing my essay.
- Have you read through the article I left you?
(a) Earl drove _____ a red light.
(b) Merdine _____ a coin into the fountain and made a wish.
(c) I’m _____ listening to your excuses.