在於

在于
zàiyú
  1. to rest with; to lie in; to be due to (a certain attribute)
  2. (of a matter) to be determined by; to be up to (sb)

CEDICT

Entry Composition

1 在 zài
  1. to exist; to be alive
  2. (of sb or sth) to be (located) at
  3. (used before a verb to indicate an action in progress)
2 於 yú
  1. (of time or place) in; at; on
  2. (indicating any indirect relation) to; toward; vis-à-vis; with regard to; for
  3. (indicating a source) from; out of
  4. (used in comparison) than
  5. (used in the passive voice) by