这道题不太理解 求解释

Passive获得指数头寸的方法有：Pure indexing；Enhanced-indexing（Stratified sampling）

除了以上方法，还有Alternative获得Passive投资指数的三种方法：

1. bond mutual fund
2. ETF
3. Synthetic means such as index-based total return swaps

具体要看题干描述，想要哪种方法。

Ruelas also tells Maestre that he has considered moving to a passively managed bond portfolio. He is not convinced it is worth his or his staff’s time and effort to try to beat the broad market bond index.

确定是要用Passive方法，放弃Active的方法，以上5个策略都有可能。

He is concerned, however, that it may be no less expensive either in time or transaction costs to replicate an index than to actively manage a portfolio.

也就是说，他认为跟踪模拟指数的方法，和Active管理的方法一样浪费钱和时间。放弃Enhanced-indexing，与Pure indexing。

Maestre recommends a bond indexing strategy，然后推荐了指数投资方法。

所以根据题干，排除Active。同时排除Pure indeng与Enhanced indexing（Stratified sampling），因为这是跟踪指数的方法。

最后，就能只能Alternative获得指数投资的方法里挑了。当然这道题是让选Least likely，那就直接是A了。