Most have 4, two have none and more than one have 8, what are they

hints: each one has its own name
they all vary in size
some students stress about remembering them for an important test
none of them existed until the late 1700s

The service industry in the united states grew in the late 1800s. what was one effect of that growth? the number of people with jobs in factories as unskilled workers decreased. the number of people with jobs in factories as unskilled workers increased. the middle class grew as people took jobs as clerks, lawyers, and teachers. the middle class shrank as people left jobs as clerks, lawyers, and teachers.