订阅的方法适当地称为“订阅”，并要求有两个数组参数。

The method for subscribing is aptly named "subscribe" and requires two parameters, both arrays.

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我们在options数组参数中设置trace选项，将该参数传递给SoapClient构造函数。

We set the trace option in an options array parameter, which we pass to the SoapClient constructor. We modify our use of the constructor to.

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这个额外的参数就是数组中的下标。

The extra parameter is the index in the array.

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