Answer:
Detect: Bulb
Transform: Mercury
Output: Reading on the tube.
Explanation:
The part of a mercury-in-glass thermometer that corresponds to the detect component is the bulb (of a high termal conductivity, metal or thin glass), which allows the mercury to be at the same temperature of the medium to measure.
Mercury is the transform component, as it expands when heated and compress when cooled.
The reading on the tube is the output, to know the temperature we have to look the reading at which the top of the mercury column is.