Automation System
Light sensors:

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

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Automation System
Stepping motors:

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

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Automation System
A venturi tube:

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

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