Faulty pronoun reference

The pronoun's antecedent (the word it replaces or refers to) should be unambiguous.

example: The lion sat beneath the tree; it was old and weak. The pronoun is it, but is the antecedent lion or tree? Only the writer knows.

example: Lions a) hunt on the plains and b) exhibit complex social behavior; that is why I study them. Does the pronoun that refer to a, b, or both?

example: The soil fauna plays an important role in the mineralization of organic matter through its feeding and locomotory activity. Does its refer to organic matter or fauna?