Final answer:
The quarrier keeps repeating the process of making shells, indicated by the foreman, until they become familiar with it and can do it independently. This repetition suggests that other machines of its class also require repetitive practice.
Step-by-step explanation:
The quarrier keeps repeating the process of making shells, demonstrated by the foreman, until they become familiar with it and can do it independently. This repetition indicates that other machines of its class, like the quarrier, also require repetitive practice to become skilled at their tasks. It suggests that these machines are designed to perform specific functions repeatedly and efficiently.