In the sentence extracted from biomedical literature, identify all the chemical entities. The required answer format is the same sentence with HTML <span> tags to mark up specific entities. 
### Entity Markup Guides:
Use <span class="chemical"> to denote a chemical.

### Input Text: To test the validity of the hypothesis that hypomethylation of DNA plays an important role in the initiation of carcinogenic process , 5 - azacytidine ( 5 - AzC ) ( 10 mg / kg ) , an inhibitor of DNA methylation , was given to rats during the phase of repair synthesis induced by the three carcinogens , benzo [ a ] - pyrene ( 200 mg / kg ) , N - methyl - N - nitrosourea ( 60 mg / kg ) and 1 , 2 - dimethylhydrazine ( 1 , 2 - DMH ) ( 100 mg / kg ) .
### Output Text:
To test the validity of the hypothesis that hypomethylation of DNA plays an important role in the initiation of carcinogenic process , <span class="chemical">5 - azacytidine</span> ( <span class="chemical">5 - AzC</span> ) ( 10 mg / kg ) , an inhibitor of DNA methylation , was given to rats during the phase of repair synthesis induced by the three carcinogens , <span class="chemical">benzo [ a ] - pyrene</span> ( 200 mg / kg ) , <span class="chemical">N - methyl - N - nitrosourea</span> ( 60 mg / kg ) and <span class="chemical">1 , 2 - dimethylhydrazine</span> ( <span class="chemical">1 , 2 - DMH</span> ) ( 100 mg / kg ) . 