Do nothing,
killing up to millions in a standard invasion, and maybe 100's of millions if it caused WW3, just isn't worth a few lousy oil tankers which aren't even ours in the first place.
There will be no WWIII over Iran.
Really?
If Russia & China back Iran, which has been a theorized issue for decades,
then
we'd probably get Russia & China backing up & pushing up their proxies in & around Iran,
Just like in the Vietnam war.
That's
the more likely & better case scenario
The
worst case scenario of course is that Russia & China bring troops into Iran, sure it's not as likely, but still a possibility.