The answer is, or should be, B. An 'adjective phrase' (or adjectival phrase) is a phrasewhose head word is an adjective, e.g. fond of steak, very happy, quite upset about it, etc.
It acts as a collection of "puzzle pieces" that will complete the larger picture.
The change in temperature is greater when the water is heated with the use of the fire caught by the food substance, then the energy content in the food substance is higher because the heat energy is greater, since the heat energy is absorbed by the water when the fire is kept under the test tube containing water. The formula indicates that if the change in temperature is greater when the mass of the substances and the volume of water are constant, then the heat energy is higher.
(The) needs to be capitalized
