anchor.diff:    You'll write a method for the `HeroListComponent` to call, a `create()` method, that takes
     just the name of a new hero and returns an `Observable` of `Hero`. It begins like this:
   
  -  我们将为`HeroListComponent`创建一个简单的`addHero()`方法，它将接受新英雄的名字：
  +  我们将为`HeroListComponent`创建一个简单的`create()`方法，它将接受新英雄的名字，并且返回一个`Hero`型的`Observable`，代码如下：
   
   +makeExample('server-communication/ts/src/app/toh/hero.service.ts', 'create-sig')(format=".")
   
  
positive.code: 
    Now that you know how the API works, implement `create()` as follows:
  
    现在，知道了这个 API 如何工作，我们就可以像这样实现`addHero()`了：
  
  +makeExample('server-communication/ts/src/app/toh/hero.service.ts', 'import-request-options', 'src/app/toh/hero.service.ts (additional imports)')(format=".")
  +makeExcerpt('src/app/toh/hero.service.ts', 'create')
  
  a#headers
  
negative.code: h3 #[b HeroListComponent] error handling
  
  h3 #[b HeroListComponent] 错误处理
  
  block hlc-error-handling
    :marked
      Back in the `HeroListComponent`, in `heroService.getHeroes()`,
  