rails 第一个程序出错

错误如下
MissingSourceFile in SayController#hello
no such file to load -- sqlite3
RAILS_ROOT: d:/demo


This error occurred while loading the following files:
 sqlite3
Request
Parameters:

None

Show session dump

---
flash: !map:ActionController::Flash::FlashHash {}


Response
Headers:

{"cookie"=>[],
"Cache-Control"=>"no-cache"}