【正确答案】 D

【答案解析】解析：句意：它们是用来将食物转换成能量、维持身体机能的。A：move or cause to move from oneplace to another,especially over a small distance转移，移动。B：move or Cause to move to another group，occupation or service(使)改行，调动。C：change or cause to change in character or composition，typically in a comparatively small but significant way(尤指以微小但显著的方式)改变性质或成分。D：make a thorough or dramatic change in the form，appearance，or character of通过深刻或剧烈的变化而改变其形式、外表或本质，彻底改变，使发生巨变，使改观，变革。