Automation System
Light sensors:

cannot be used a s limit switches.
never use infrared light as light source
come in a wide variety of mounting styles
work in direct sunlight
None of these

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Automation System
Stepping motors:

All of these
can be built to index different amounts by changing the pole configuration
can run both clockwise and counterclockwise
can run at varying speeds
do not require commutators

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Automation System
A venturi tube:

can be used to measure gas or liquid flow rates
is made only of metal
None of these
is extremely difficult to use
measures the presence of a liquid

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