Fill in the blank with an appropriate option. David always kept his ______ open for anything that might put them at risk.

eagle eyes

The correct option to fill in the blank is eagle eyes.

• Black eye is a bruise around the eye. It is not the most appropriate word to use in this context, as it does not refer to being alert or watchful.
• Starry eyes is a term used to describe someone who is looking at something with love or admiration. It is not the most appropriate word to use in this context, as it does not refer to being alert or watchful.
• Sheep eyes is a term used to describe someone who is looking at something with fear or timidity. It is not the most appropriate word to use in this context, as it does not refer to being alert or watchful.
• Eagle eyes is a term used to describe someone who is very observant or watchful. It is the most appropriate word to use in this context, as it refers to David being alert and aware of his surroundings.