sunk vs sank?

I think it should be sank. If you look at your verb columns, then verb 2 will be sank and verb 3 will be sunk. A bit like swim, swam, swum.

In your sentence you are using the past simple, so it should be sank.

swam or had swum ("had" is what we used to call a "helper verb."

Anonymoussunk or sank

There are four irregular verbs that allow either "a" or "u" in the simple past form. It all depends on what the speaker is used to. sink, shrink, stink, spring. Personally I only use the "a" in sank.

CJ

Thank you CalifJim for clarifying, or should I say correcting. I would say "stank" and "sank", but probably not shrank. Not sure about sprang.

This is probably way out of date, but I just saw this.

CJ, the information you gave is incorrect. There are different forms for a reason, each indicating a different time in which the action takes place.

Sink = present tense
I sink in water.
Sank = past tense
I sank his battleship.
(has/have | had) Sunk = perfect | pluperfect tenses
He has sunk

AnonymousCJ, the information you gave is incorrect.

Yours is an extremely prescriptive v

http://dictionary.cambridge.org/dictionary/british/sink agrees that the past can be 'sank' or 'sunk in AmE.

ok

i had a bad week, no doubt that next week it will be the same, so it sucks to be me

It is 'you sank your teeth'

You use 'sunk' after have/had because it is the past participle.
e.g. I had sunk my teeth into...