-- Diabetics experience fatigue (tiredness) because glucose (which is the key source of energy) can't get into the cells. (fullhealthsecrets.com)
At least Johnson appears comfortable with the uneven tone, providing the key source of energy and entertainment in the otherwise unexciting offering. (trespassmag.com)
«Even if oil will remain the key source of energy for the foreseeable future, there is, nevertheless, growing evidence that the fossil - fuel era has passed its peak.» (wardsauto.com)