adj. , determiner , pronoun
1) ~ for (that's ~ for me)
2) ~ to + inf. (it's ~ to know that they are safe; we've had ~ excitement to last a lifetime)
3) ~ of (~ of them)
USAGE NOTE: The use of the preposition of is necessary when a pronoun follows. When a noun follows, the use of of the limits the meaning
--we have seen ~ documentaries; we have seen ~ of the documentaries that we had discussed earlier.