REMEMBER: The stem of a verb is the part of the infinitive that is left after you drop the endings -ar, -er, or -ir.
For example, the stem of poder is pod- Stem changing verbs have a spelling change in their stem in all forms of the present tense except the nosotros(as) and vosotros(as) forms.
Yo_____(poder)(-o -ue) memorizar el vocabulario de español.