The present perfect simple expresses an action that is still going on or that stopped recently, but has an influence on the present. We use the Present Perfect to say that an action happened at an unspecified time.

This is the final monograph published for what has been perhaps the largest and most complex research investigation ever attempted on the far-reaching impacts of information and information resources on the political, ...

In the province of Chimborazo at the Experimental Station Tunshi, belonging to the Faculty of livestock Sciences at Escuela Superior Politecnica de Chimborazo was made a very important study to know the effect of the ...

Executive summary The main objective of this study on 'Growth and Employment' is to determine the ability of the Jamaican economy to generate productive employment, and how this has been affected by reforms implemented in ...

This paper asks whether the recent trade liberalization in Argentina, Brazil and Mexico has led to increased transfer of polluting activities to Latin America. Using a factor content of trade approach, it shows that prior ...

La erosión como consecuencia de la degradación del suelo especialmente en ladera, ocasiona pérdida de la capa vegetal, baja capacidad de retención de agua, decrecimiento de la productividad y baja rentabilidad de los ...

In this research work has been proposed the synthesis of Gallium Nitride Nan-owires, which is a semiconductor that has gained much importance in recent years due to its properties that allow it to be used in high performance ...