这到底是为啥啊，字数不够字数不够？

在看node.js开发指南 做书上那个例子，mongodb是启动了 但是运行还是报错

C:\Node\Microspace>node app.js

module.js:340
    throw err;
          ^
Error: Cannot find module 'bson'
    at Function.Module._resolveFilename (module.js:338:15)
    at Function.Module._load (module.js:280:25)
    at Module.require (module.js:362:17)
    at require (module.js:378:17)
    at C:\Node\Microspace\node_modules\connect-mongo\node_modules\mongodb\lib\mo
ngodb\index.js:36:22
    at Array.forEach (native)
    at Object.<anonymous> (C:\Node\Microspace\node_modules\connect-mongo\node_mo
dules\mongodb\lib\mongodb\index.js:26:25)
    at Module._compile (module.js:449:26)
    at Object.Module._extensions..js (module.js:467:10)
    at Module.load (module.js:356:32)