Question

inventors often follow these steps.
why was it a problem to open and shut elevator doors by hand?
a person might decide to close the elevator’s outer door , because someone could step into the elev have to wait.
key ideas
the text says
if the doors to the elevator shaft were left open, people were at risk of falling in.
i already know
falling from a high place can lead to serious injuries.

Explanation:

To answer why opening and shutting elevator doors by hand was a problem, we use the key ideas: the text says if elevator shaft doors were left open, people risked falling in, and we know falling from height causes serious injuries. So manual door operation risked people forgetting to close doors, leading to falls and injuries.

Answer:

Opening and shutting elevator doors by hand was a problem because a person might forget to close the elevator’s outer doors (or the doors to the elevator shaft), and if those doors were left open, someone could step into the elevator shaft and fall from a high place, which can lead to serious injuries.