A man who connives . . . . . . . . the faults of his children is their worst enemy.

with
at
of
on

The correct answer is: C. of

To connive means to secretly plan or help to do something wrong or harmful. So, a man who connives at the faults of his children is their worst enemy because he is secretly helping them to do wrong.

The other options are not correct because they do not make sense in the context of the sentence.

  • Option A: “with” does not make sense because it suggests that the man is working together with his children to do wrong.
  • Option B: “at” does not make sense because it suggests that the man is angry or annoyed at his children’s faults.
  • Option D: “on” does not make sense because it suggests that the man is putting his children’s faults on display.