How can I show that i was under my parents medical health care coverage in the 1040ez

[Vanessa]

If you were claimed as a dependent you will not need to answer that question.  You will get to a screen that tells you, "Since someone can claim you on their 2017 taxes, you don't have to complete Health Insurance"

If no one can claim you on their return, then all you need to do is answer Yes, when asked if you were insured all year and no, it was not Obamacare, (if it was not) then that is all the information you will need to enter.  

If they have insurance on you through the Marketplace.  Then you will need information from their 1095-A and may need to allocate a percentage of the premiums to you. https://taxmap.irs.gov/taxmap/instr2/i8962-006.htm