U.S. employers spend a considerable amount of time and resources on both formal and informal training including safety training. A national survey found establishments with 50 or more employees paid $7.7 billion to in-house training staff and $5.5 billion to outside trainers in 1994, $139 and $98 per employee respectively [2].
选项：

A:Quotes from publications;
B:Example;
C:Expert testimony;
D:Experience