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: Maximal twitches of the diaphragm were lower in the C group ( 653 + / - 174 g / cm ( 2 ) ) than in the M group ( 837 + / - 171 g / cm ( 2 ) ; p < 0 . 05 ) and the T group ( 765 + / - 145 g / cm ( 2 ) , NS ) .
### Output Text:
Maximal twitches of the diaphragm were lower in the C group ( 653 + / - 174 g / cm ( 2 ) ) than in the <span class="chemical">M</span> group ( 837 + / - 171 g / cm ( 2 ) ; p < 0 . 05 ) and the <span class="chemical">T</span> group ( 765 + / - 145 g / cm ( 2 ) , NS ) . 