Alternative 2 is correct. When the Main Ice Sheet melted more than 12 800 years ago, meltwater-rivers were formed.  They were under high pressure in and beneath the glacier and could flow as whirlpools towards the bottom and “drill” circular holes in the bedrock, as a gigantic drill. The meltwater contained finer particles from the glacier, which contributed as abrasive.

Why are the other answers wrong?

(1) A large meteorite impact would have left traces. Here is only  the local granitic gneis.

(3) There have been no mining in the area.

(4) An entertaining idea. In old days some people actually believed that trolls had made the holes and used them as kettles, and they are therefore named Giant (troll) kettles.