Choice-'a' is a slippery, misleading, ambiguous statement,
but it's less wrong than any of the other choices on this list.
Answer:
cold water strengthens the magnetic attractive force.
Explanation:
The molecules within the magnet will move slower because they have less kinetic energy,so there is less vibration within the magnets molecules.
To develop this problem it is necessary to apply the concepts related to Sound Intensity.
By definition the intensity is given by the equation

Where,
I = Intensity of Sound
= Intensity of Reference
At this case we have that 15 engines produces 15 times the reference intensity, that is

And the total mutual intensity is 100 dB, so we should




Therefore each one of these engines produce D. 88dB.
The distance the spring stretches is the answer.
I hope this helps.
Have a nice day.
The answer is C! I knew this way before taking the test