In creating a model of out living planet, scientists need to consider four major Earth systems. Briefly describe these four system, and then explain
why it is difficult to study these systems individually.

not too sure maybe olecranon process

this website is for anybody really not just for girls just saying, also while a lot of males are mean and you know there are the few who are kind and then there's the nice-guys but then theirs also guys like me who are shy we don't get out much because there are people like you who exist who would most likely punch a guy in the face so next time just think about things before you post them to a website where guys and girls can see your question.

69 is the correct math for the amino acids