It MUST be either glue or gravity.
Answer:
=20 turns
Explanation:
The given case is a step down transformer as we need to reduce 120 V to 6 V.
number of turns on primary coil N_{P}= 400
current delivered by secondary coil I_{S}= 500 mA
output voltage = 6 V (rms)
we know that

putting values we get


to calculate number of turns in secondary

therefore,
=20 turns
I'd guess at valve B. more information about the interesting question would help.
Temperature difference is required, so i’m guessing - a. thermometer - would be required to check that temperature.
The answer is the 4th option because they don't use oxygen, that's what they produce