Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The Broad Line Region of Quasars   The last decade saw long-awaited improvements in our understanding of active
galactic nuclei (AGN) spectral properties. This contribution reviews some
important observational results obtained from optical and UV data as well as
constraints on physical parameters that control the structure and dynamics of
the Broad Line Region.

24
The categories of this paper are: dg-ga
35
The categories of this paper are: mtrl-th
10
The categories of this paper are: q-bio
13
The categories of this paper are: quant-ph
16
The categories of this paper are: stat
15
The categories of this paper are: nucl-ex
9
The categories of this paper are: nlin
21
The categories of this paper are: adap-org
30
The categories of this paper are: q-alg
20
The categories of this paper are: acc-phys
26
The categories of this paper are: bayes-an
36
The categories of this paper are: cmp-lg
3
The categories of this paper are: physics
2
The categories of this paper are: math
14
The categories of this paper are: math-ph
11
The categories of this paper are: hep-lat