German Present Tense – Verbs with Vowel Shift

Which of the following statements about this whole vowel shift issue are WRONG? (multiple answers)

What do the following verbs have in common:
fallen (to fall) , sagen (to say) , warten (to wait)?

Which of these verbs might get a vowel change for “du” and “er/sie/es”? (multiple answers)

Which of these verbs gets a vowel change for “ich” and “du”?

The verb “sehen” (to see) gets a shift. What’s the proper translation for:
“She sees a tree.“

Now it’s your turn!  “essen” (to eat) gets a change. Conjugate it :)!

And one last question:
what’s the proper reaction if I tell you that sometimes (very very sometime), there are some more changes to the stem.
Like for “nehmen” we have “ich nehme” but “du nimmst”, “er nimmt”