[译] 高效发动机节省燃料。
[误] An efficient engine is economic of fuel.

[正] An efficient engine is economical of fuel.
[注] 形容词 economical (= careful in the spending of money, time, etc.) 意为"节省的"、"经济的"，例如：This stove is economical of fuel. 这种灶节省燃料。/She is an economical housekeeper and feeds her family cheaply. 她是一位节俭的家庭主妇，全家吃得很省。economic（= of economics）意为"经济（学）的"、"经济（上）的"。例如：The country is in a bad economic state, so they must reduce profits. 该国经济状况不佳，所以他们须降低利润率。/She majored in economic history. 她专修过经济史。