In the past, many children didn't even go to school - they went to work in a factory or other job (yes, even 6-10 year olds!). After the Industrial Revolution, people decided that kids needed to be educated, and started more schools for them instead of making them work so hard. They did most of the work in the school just because paper was so expensive. Each child would have a slate, or small chalkboard, that they could take home and work out problems on. What you think of as "modern" homework started around the turn of the century as schools became more of what you're familiar with.
I´d say they´ve decreased.
decreased
Decreased.
It has decreased.
increased
The individual heartbeat, or contraction, can be modified by input from the sympathetic and parasympathetic nervous systems. This modification can include increased or decreased contraction ratios, increased or decreased stroke volume and increased or decreased rate of contraction.
Increased.
Decreased.
Decreased
it has increased nd decreased depending on what animals and regions
The individual heartbeat, or contraction, can be modified by input from the sympathetic and parasympathetic nervous systems. This modification can include increased or decreased contraction ratios, increased or decreased stroke volume and increased or decreased rate of contraction.
Increased