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: Most of the other low testosterone levels seemed to result from nonorganic hypothalamic dysfunction because of normal serum luteinizing hormone and prolactin and to have only a small role in erectile dysfunction ( definite improvement in only 16 of 44 [ 36 % ] after androgen therapy , normal morning or nocturnal erections in 30 % and definite vasculogenic contributions in 42 % ) .
### Output Text:
Most of the other low <span class="chemical">testosterone</span> levels seemed to result from nonorganic hypothalamic dysfunction because of normal serum luteinizing hormone and prolactin and to have only a small role in erectile dysfunction ( definite improvement in only 16 of 44 [ 36 % ] after androgen therapy , normal morning or nocturnal erections in 30 % and definite vasculogenic contributions in 42 % ) . 