If I want to become a mechanicalengineer, what whould I choose biology or computer. Need your Advie?

Any science subject is an advantage, but IT is an increasing part of engineering from the design & development phase (CAD, like solid modeling CATIA, Solid Works, & 3D printing,) Production side CAM such as integrated company systems provided by SAP) and ultimately of course to the marketing & support of the final product to the customer.