Liam Hemsworth -- About Miley Cyrus' Engagement Ring ...

First Miley Cyrus' engagement ring returned ... now Liam Hemsworth is back -- but whether their engagement is back on is the big question, and we posed it directly to Liam.

Hemsworth arrived at LAX last night after a THREE WEEK trip to Australia and the Philippines ... sans Miley, and on the heels of rumors he and January Jones had a fling.

We asked Liam about everything from Miley's disappearing and reappearing diamond ring ... January (the month and the chick) ... and even the quality of gnar Down Under.