统计一段文本中各个单词出现的频次。
文本："She sells seashells by the seashore. The shells she sells are surely seashells."
She: 1  
sells: 2  
seashells: 3  
by: 1  
the: 2  
seashore: 1  
The: 1  
shells: 2  
are: 1  
surely: 1