Which nutrient is the most important one for our body and comprises one third of our bones

Calcium! 
because it keeps our bones healthy and strong.
People usually get calcium from dairy products. For example, milk, cheese, and butter. If you eat a good portion of dairy products then your not so prone to broken bones and you will have a healthy bone:)
anyways hope i helped
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Yeah, the answer is definitely b.assuming that you're a high school student or middle school student, you probably don't need your parents' to pick out your clothes anymore. and i don't know how it works at other schools, but i know that at my high school, you don't get to pick the book you read for an english assignment. your teacher picks that. the decision of what after-school job i should get, i would definitely make with from my parents and other people that i trust. ultimately, the decision is up to me, but i would need advice from people who are more experienced.