Once the causes of a problem with a product are identified, the next step is to a.
communicate the solution.
b.
identify a need.
c.
redesign the product.
d.
build a prototype.

before we can answer, we have to see the choices that are printed there with the question.   that's the only way we can point you to the correct one.

coil wire, increase current, put iron inside the coil

ammonium chloride & tallow

graph slopes whilst gas cools, then it is flat whilst conensation to liquid happens, the coolong liquid then graphs as a slope when it solidifies graph is flat

latent heat