生成一个由50个单词组成的随机句子，每个单词应该由字母和数字组成。
1. Generate a random string of 50 alphanumeric characters.
2. Split the string into words by using regex to match groups of consecutive letters and/or numbers.
3. Join the resulting list of words with spaces to form a sentence. 
4. Repeat steps 1-3 until a satisfactory sentence is produced.