Questions & Answers about Prefiero esta tela para la blusa.
Because preferir is a stem-changing verb in the present tense. In most present-tense forms, the e in the stem changes to ie:
So prefiero means I prefer.
Spanish often leaves out subject pronouns when they are not needed, because the verb ending already shows who the subject is. Prefiero already tells us the subject is I.
You can say Yo prefiero esta tela para la blusa, but the yo is usually only added for emphasis, contrast, or clarity.