Risks can accumulate over time through exposure to different things over life which is a normal part of life generally. People who do a lot of crazy things are people who are more prone to having different kinds of risks being brought upon them. If you're working as a construction, it's more likely with time that you will suffer from some sort of work-related accident than someone who works in an office all day long.
They are basically the same thing
Brachial plexus. The brachial plexus is a group of nerves that control the muscles of the shoulder, arm, forearm, and hand.
I'd have to say d. the hand, because every human (for the most part, no offence intended to anyone) has a hand and is able to make good (or bad, rather) use of it. It's what a person always has access to at any given time or place, even if they don't have access to one of the other options.
Substance abuse such as drugs, alcohol and tobacco, family problems such as domestic violence and abuse, social problems such as peer pressure, bullying, and exclusion, and so many other environmental reasons, but substance abuse, family dysfunction and social problems are the common reasons why.
