托人從國內帶胰島素，因我媽有糖尿病，
-You may need to the Dr. letter/certification that this kind of medicine is specific fo ryou mother's 糖尿病, so if the CBP officer ask, show the Dr. letter and explain it.
給海關官員寫信，該怎麽寫？
-May introduce your mother's 糖尿病 situation briefly and conscisely, and say because the insurance in China does not cover the medicine fee in US, your mother has to purchase this kind of medicine in China and ask your friend to bring it to your mother, etc.
