De la Cruz, Efren <br/><br/>
Strategic intervention materials on ecological concepts 
Efren de la Cruz 
 -  2007 
 - xii, 172 leaves  28 cm. 
<br/><br/> Thesis (M.A.Ed-Biology) -- Mariano Marcos State University-Graduate School, Laoag City 
<br/><br/>Bibliography: leaves 141-143