What does it mean when some psychologists support the idea that people experience a series of independent steps or stages?

People want to be independent and they try to remain independent because it makes people feel like they have more control in their lives that is why it starts in stages of for example choosing your own clothes or outfit as a child and will eventually grow into moving out of your parent's house and living on your own. 

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(a) is not correct because one does not get increased cholesterol  from lifting weights.(b) is not correct because lifting weights cannot reduce the risk of a hereditary disease.(c) is not correct because back pain isn't a benefit! and plus, if he lifts weights properly, he should not have back pain.(d) is the correct answer because his ligaments will gain mass, making it easier for him to carry heavier weights and he will also be stronger!