Classifying Verbs that are Stem-Changing in Present Tense

If a verb is "stem-changing" (or a "boot" verb), the vowel in the stem (first part of verb) is replaced by the new vowel or vowels with all pronouns EXCEPT nosotros/as and vosotros/as. In other words, they change in the boot. (Ask your teacher if you don't know what that means!) The endings of the verbs will stay the same according to whether they are - ar, -er, or -ir verbs. A couple of hints to remember:
1) If there are two "e"s in the stem, like "entender" and "preferir", the second "e" changes, but not the first .
Example: prefiero, prefieres, prefiere, preferimos, preferís, prefieren
2) "reír" and "sonreír" need an accent mark over the stressed vowel - they will conjugate the same. Ex - río, ríes, ríe, reímos, reís, ríen
3) "Seguir" does not need the "u" in the "yo" because it will change the sound - sigo, sigues, sigue, seguimos, seguís, siguen