Would of, could of, and should of are never right on ACT English. The words are would have, could have, and should have — or the contractions would've, could've, and should've. The of is a sound-alike for the unstressed have. Diction items like this are in word choice on ACT English.
Expand the contraction
I would've finished the section means I would have finished. There is no verb of hiding in there. If an answer writes would of finished, it is wrong even if the rest of the sentence is clean.
Apostrophes in real contractions are covered in apostrophes. The neighbor that looks similar is its versus it's, where the apostrophe also stands for missing letters.
The bottom line
If you hear “would of,” write would have or would've. Cross out any choice that uses of as the helping verb. The grammar map is in ACT grammar rules.
Start practicing
Start with a free diagnostic, then drill your weak spots with 15-question quizzes and track how you're doing across Reading, English, and Math. Compare plans whenever you're ready to go further.
This article offers general ACT prep guidance. The ACT can change from year to year, including its format, scoring, policies, test dates, and fees, so always confirm the latest details on the official ACT website at act.org before you make decisions. ACT® is a registered trademark of ACT, Inc. thirty-six is not affiliated with, endorsed by, or sponsored by ACT.