Choice A rationale:

While a tuberculin syringe can be used for insulin administration, it’s not necessary when mixing NPH and regular insulin. Insulin syringes are typically used for this purpose.

Choice B rationale:

Injecting air into each vial before withdrawing insulin helps equalize pressure and makes it easier to draw up the insulin. This should be done before withdrawing any insulin.

Choice C rationale:

Withdrawing NPH insulin first contradicts the standard practice of drawing up insulins. The usual recommendation is to draw up short-acting (regular) insulin before intermediate-acting (NPH) insulin.

Choice D rationale:

Shaking the regular insulin vial is unnecessary and could potentially create bubbles, making it harder to draw up the correct dose of insulin.