1. 1 secondary title

1. 1. 1 tertiary title

2. Headlines

2. 1 secondary title

2. 1. 1 three-level title

2.2 secondary title

2.2. 1 level 3 title

2.2.2 Three-level titles

2.2.3 Three-level titles

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For example:

1 research results

1. 1 general situation of freshmen's school adaptation.

1.2 demographic variables and the adaptation of freshmen in senior high school

1.2. 1 Differences in school adaptation of freshmen of different sexes

1.2.2 differences in school adaptation between only-child and non-only freshmen in senior high school

1.3 school factors and the school adaptation of freshmen in senior high school

1.3. 1 Differences of freshmen's adaptation between key schools and non-key schools

1.3.2 differences in school adaptation between residents and non-resident freshmen.