给定一个文章，返回其中每个单词的词频。
"The quick brown fox jumps over the lazy dog. The lazy dog, peeved to be left behind, gets its revenge  months later when he eats the casserole the brown fox is saving for his cub."
the: 3
quick: 1
brown: 2
fox: 2
jumps: 1
over: 1
lazy: 2
dog: 2
peeved: 1
to: 1
be: 1
left: 1
behind: 1
gets: 1
its: 1
revenge: 1
months: 1
later: 1
when: 1
he: 1
eats: 1
casserole: 1
is: 1
saving: 1
for: 1
his: 1
cub: 1.