Multiple choice Directions: Fill in the blank with the correct word. As ________ as nails. hard firm strong rigid Reveal answer Fill a bubble to check yourself A Correct answer Explanation The correct answer is 'hard' because 'hard as nails' is a common idiom describing someone tough, unfeeling, or something very durable. 'Strong' and 'rigid' are related but 'hard' is the established word in this expression.