Given a fact, create a question that can be answered using the fact. Construct the question such that it is unambiguous, has a unique answer and the answer can be given using the fact.

Fact: a hot substance is a source of heat
Water can be boiled in a pot over a?

Fact: as temperature increases , the ability of that liquid to dissolve solids will increase
As water gets warmer?

Fact: a toaster converts electrical energy into heat energy for toasting

a toaster converts electricity into radiant waves for?