在完成Ruby on Rails 教程第 3 章的 RVM 设置、rspec 和保护部分之后，每当我运行时，bundle install我都会收到以下错误转储：
Gem::Installer::ExtensionBuildError: ERROR: Failed to build gem native extension.
/usr/bin/ruby1.9.1 extconf.rb
/usr/lib/ruby/1.9.1/rubygems/custom_require.rb:36:in `require': cannot load such file -- mkmf (LoadError)
from /usr/lib/ruby/1.9.1/rubygems/custom_require.rb:36:in `require'
from extconf.rb:5:in `<main>'
Gem files will remain installed in /home/dan/.bundler/tmp/17577/gems/nokogiri-1.5.2 for inspection.
Results logged to /home/dan/.bundler/tmp/17577/gems/nokogiri-1.5.2/ext/nokogiri/gem_make.out
An error occured while installing nokogiri (1.5.2), and Bundler cannot continue.
Make sure that `gem install nokogiri -v '1.5.2'` succeeds before bundling.
在 gem_make.out 中：
Gem::Installer::ExtensionBuildError: ERROR: Failed to build gem native extension.
/usr/bin/ruby1.9.1 extconf.rb
/usr/lib/ruby/1.9.1/rubygems/custom_require.rb:36:in `require': cannot load such file --mkmf (LoadError)
from /usr/lib/ruby/1.9.1/rubygems/custom_require.rb:36:in `require'
from extconf.rb:5:in `<main>'
我已经调试了一段时间，我想我被卡住了。帮助将不胜感激！