Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The composition of cosmic rays at the knee   The present experimental status concerning the composition of cosmic rays in
the PeV region is reviewed. The results are compared to predictions of
contemporary models for the acceleration and propagation of galactic cosmic
rays.

7
The categories of this paper are: hep-th
36
The categories of this paper are: cmp-lg
22
The categories of this paper are: chao-dyn
31
The categories of this paper are: ao-sci
15
The categories of this paper are: nucl-ex
4
The categories of this paper are: cond-mat
2
The categories of this paper are: math
19
The categories of this paper are: eess
11
The categories of this paper are: hep-lat
13
The categories of this paper are: quant-ph
21
The categories of this paper are: adap-org
9
The categories of this paper are: nlin
8
The categories of this paper are: hep-ex
0
The categories of this paper are: hep-ph
29
The categories of this paper are: funct-an
14
The categories of this paper are: math-ph