[求助]向大侠致敬！请教一道题

Y has been believed to cause Z. A new report, noting that Y and Z are often observed to be preceded by X, suggests that X, not Y, may be the cause of Z.

Which of the following futher observations would best support the new report's suggestion?

A In cases where X occurs but Y does not, X is ususally followed by Z.

B In cases where X occurs, followed by Y, Y is usually followed by Z.

C In cases where Y occurs but X does not,Y is usually followed by Z.

D  In cases where Y occurs but Z does not,Y is usually followed by X.

E  In cases where Z occurs, it is usually preceded by X and Y.

答案选A,完全没有思路，请路过高人多多指点，不胜感激！！！

原来认为y导致z，现在一个新报告称，x发生在y,z之前且是x导致了z。问支持。答案要点一定是：由原因且只有一个（x）有结果（z）

A可以， y没发生，x在z前，就有可能是x导致了z

B, xy都发生了，且都在z之前，无关

C, x没发生，削弱

D, z没发生，没有结果，无关

E, xy都发生了，无关。