What version 1.x does jquery choose? 2.x? 3.x?

There are currently three major versions of jquery:

1.x: Compatible with ie678, the most widely used, the official only bug maintenance, function no longer new. So for general projects, the 1.x version is available, and the final version: 1.12.4 (May 20, 2016)
2.x: Incompatible with ie678, few people use, official only bug maintenance, function no longer new. If you do not consider a compatible low version of the browser can use 2.x, final version: 2.2.4 (May 20, 2016)
3.x: Incompatible ie678, only the latest browser is supported. Except for special requirements, the 3.x version is generally not used, and many old jquery plugins do not support this version. Currently this version is the official maintenance version of the main update.

1.X Large version, the subdivision version is very many, each version of the function will have a certain difference. Many of the tutorials you see online are mostly 1.x versions. Official jquery Handbook: http://api.jquery.com/

Maintenance ie678 is the opinion headache thing, generally we will load a CSS and JS alone processing. Fortunately, the use of these browsers are gradually reduced, computer-side users have gradually been replaced by mobile users, if there is no special requirements, will generally choose to abandon the ie678 support.

More friendly prompt user to upgrade browser code (PC side)
Happy browsing: http://browsehappy.osfipin.com/. The code in the upper right corner, click on the pop-up window to view.

What version 1.x does jquery choose? 2.x? 3.x?