when a forensic analyst determines the chemical composition of a preparation that may contain illicit drugs such as heroin, cocaine, or barbiturates, this is an example of what?

Chang because he didn't cut out the sun all together and he waited for the sunscreen to soak in before going outside. Then as the sunscreen began to wear off he added more to his body and protected his body from sunburn but still got the vitamin D he needed. Also Nathan did the same thing but used weak sunscreen and never reapplied it. Meg is using artificial light to get tan but is not getting the vitamin D her body needs. Sandy just straight up Is not getting Vitamin D.