Of course, if there is little content under the three-level heading, or there are few three-level headings that need to be discussed hierarchically, you can directly use (1) and (2) ………………………….

Generally speaking, it is common to use the four-level title 1. 1. 1 for doctoral or master's thesis, but it is rare for undergraduate/junior college graduation thesis/graduation project.

Supplement:

If it is specifically pointed out that the four-level title1.1.1is not allowed, (1)(2)(3) will be used in the three-level title.