Since this drawing is his way of reminding her that she and their garden are "as safe as a missel thrush", it makes her one of the many creatures whose secrets he keeps faithfully. So, having that in mind, I would say the correct answer is A) his trustworthiness.
When it comes is the right answer
So, you may understand what is being read or said aloud.
The Whites learn that their son Herbert is dead.
