Correct answer only !

which of the following situations does not involve potential energy being changed into kinetic energy?

So we are looking for something where both height, or elastic potential energy is present, as well as motion.

A creek flowing down a mountain has motion, as the creek is moving and from a height on the mountain so GPE is turning into KE

Shooting a dart from a spring loaded gun has KE because of the motion of the dart as well as elastic potential energy stored within the spring

An apple falling from a tree has KE as the apple falls and well as GPE because it started from at the top of the tree where height was involved.

A stretched rubber band has elastic potential energy as it has the potential to move, but there is no mention of the rubber band moving so I would have to say this would be the answer.

if the thermos has a vacuum innner, then heat through conv currents and conduction are reduced = vacuum flask