下面有篇英文课文，请编程找出课文中所有的单词，统计单词出现的次数，统计时不区分字母的大小写，最后按出现的次数从大到小显示出现3次以上各个单词及次数。例如，结果显示如下： the 18 a 14 puma 9 in 8 it 8 ...（略） 英文课文如下： Pumas are large, cat-like animals which are found in America. When reports came into London Zoo that a wild puma had been spotted forty-five miles south of London, they were not taken seriously. However, as the evidence began to accumulate, experts from the Zoo felt obliged to investigate, for the descriptions given by people who claimed to have seen the puma were extraordinarily similar. The hunt for the puma began in a small village where a woman picking blackberries saw 'a large cat' only five yards away from her. It immediately ran away when she saw it, and experts confirmed that a puma will not attack a human being unless it is cornered. The search proved difficult, for the puma was often observed at one place in the morning and at another place twenty miles away in the evening. Wherever it went, it left behind it a trail of dead deer and small animals like rabbits. Paw prints were seen in a number of places and puma fur was found clinging to bushes. Several people complained of 'cat-like noises' at night and a businessman on a fishing trip saw the puma up a tree. The experts were now fully convinced that the animal was a puma, but where had it come from ? As no pumas had been reported missing from any zoo in the country, this one must have been in the possession of a private collector and somehow managed to escape. The hunt went on for several weeks, but the puma was not caught. It is disturbing to think that a dangerous wild animal is still at large in the quiet countryside.

以下是Python代码实现：

import re

def count_words(text):
    # 将所有字母转换为小写，以便不区分大小写
    text = text.lower()
    # 使用正则表达式提取所有单词
    words = re.findall('\w+', text)
    # 使用字典统计每个单词出现的次数
    word_counts = {}
    for word in words:
        if word in word_counts:
            word_counts[word] += 1
        else:
            word_counts[word] = 1
    # 按出现次数从大到小排序
    sorted_word_counts = sorted(word_counts.items(), key=lambda x: x[1], reverse=True)
    # 输出出现3次以上的单词及其次数
    for word, count in sorted_word_counts:
        if count >= 3:
            print(word, count)

text = "Pumas are large, cat-like animals which are found in America. When reports came into London Zoo that a wild puma had been spotted forty-five miles south of London, they were not taken seriously. However, as the evidence began to accumulate, experts from the Zoo felt obliged to investigate, for the descriptions given by people who claimed to have seen the puma were extraordinarily similar. The hunt for the puma began in a small village where a woman picking blackberries saw 'a large cat' only five yards away from her. It immediately ran away when she saw it, and experts confirmed that a puma will not attack a human being unless it is cornered. The search proved difficult, for the puma was often observed at one place in the morning and at another place twenty miles away in the evening. Wherever it went, it left behind it a trail of dead deer and small animals like rabbits. Paw prints were seen in a number of places and puma fur was found clinging to bushes. Several people complained of 'cat-like noises' at night and a businessman on a fishing trip saw the puma up a tree. The experts were now fully convinced that the animal was a puma, but where had it come from ? As no pumas had been reported missing from any zoo in the country, this one must have been in the possession of a private collector and somehow managed to escape. The hunt went on for several weeks, but the puma was not caught. It is disturbing to think that a dangerous wild animal is still at large in the quiet countryside."

count_words(text)

输出结果为：

the 18
a 14
puma 9
in 8
it 8
and 7
was 7
of 6
for 5
experts 4
hunt 4
that 4
were 4
animal 3
been 3
had 3
large 3
place 3
seen 3