Although the actual questions are missing from your ask, here's how you can tell.
If the study will be messed up (added bias) through interaction with the subjects the study should be observational. For example if a biologists wanted to study the eating habits of wild birds in the tropics, they would need to do an observational study. if they did a controlled experiment, the birds will change their eating habits based on human interaction, thus making the study invalid.
If the study requires specific measurements, close monitoring, or contact and interaction with the subjects the study should be a controlled experiment. For example, if a scientist wanted to test out a new drug, the health of patients would need to be closely monitored.
Answer:
D.) Amino Acids
Explanation:
Please see picture attached to this answer.
Los aminoácidos químicamente son sustancias que estan formadas como su nombre lo indica, por un grupo amino y uno carboxilo, unidos ambos a un carbono central. Recordemos que el átomo de carbono tiene valencia 4, es decir, tiene cuatro lugares para sostener enlaces. Por lo tanto el resto los puede ocupar con átomos de hidrógeno u otras cadenas carbonadas a las que simbolizamos con la letra R. R puede ser un grupo metilo o un etilo o un gruo de más carbonos o también un anillo aromático, etc
