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: HYPOTHESIS : The aim of the present study was to review the data accumulated so far on the use of LMWH in this patient population and to discuss its applicability in common practice .
### Output Text:
HYPOTHESIS : The aim of the present study was to review the data accumulated so far on the use of <span class="chemical">LMWH</span> in this patient population and to discuss its applicability in common practice . 