I'll go with 'B' for 500 Regis, and yes, that is my final answer.

这是一个很难用汉语解释的问题，追本溯源的话应该好好理解一下效率和效果到底强调什么东西。例如一角钱买一个鸡蛋，和一角钱买两个鸡蛋。在你说话的时候到底在强调什么呢？估计你在强调一角钱的使用效果。应该是effetive。而效率的定义式单位时间内完成多少任务，应该是efficient。总不能理解成一角钱多长时间能花出去。在这三个短语中1“高效能源”，2“高效时间”，3“高效的利用钱”。1强调的是这种能源效率。2强调也是效率，而3强调的应该是效果。在你给出的例句You must ensure that you should make use of the money in an______way.我更倾向钱的使用效果。effective。

Oops! Just noticed a couple of typographical errors. I know English, but not keyboards . . . hahaha! It should have been: Hello Patricia? . . . As in all things in life, without all of the necessary information, the question cannot be fully answered. . . . The reason for this is that either A. or B. can be correct, subject to the meaning you wish to convey. . . . In your example, A. would imply, the money is to be spent to achieve the most desirable (best value) result, whereas B. would imply, the money would be spent to achieve the lowest cost (cheapest) outcome. . . . Both are correct! . . . In daily usage (including written) you would never be questioned about the subtle differences, inherent in your question. . . . Bye for now and please take care of yourself, until we meet? . . . Jon

Hello Patricia? As in all things in life, without all of the necessary information, the question cannot be answered. The reason for this is that either A. or B. can be correct, subject to the meaning you wish to convey. In your example, A. would imply, the money is to be spent to achieve the most desired (best value) result, whereas B. would imply, the money would be spent to achieve the lowest cost (cheapest) outcome. Both are correct! In daily usage (including written) you would never be questioned about the subtle differences, inherent in you question. Bye for now . . . and please take care of yourself, until we meet? Jon

A. effective