下面是一个解决方案，每行都有一些注解：

user_num =9; #Initialize a random non-native number to be able to go to the core of the while loop

while (user_num >= 0): #After each user input, check if the input is a non-negative number
  #If user input is a non-negative number, you end up here, inside the while loop
  print("Body") #This is one of the statements. It prints "Body"
  user_num = int(input())  #Acquire a new input from the user and store it in the variable user_num. At this point, the loop runs again using the new user input.
#If user input doesn't meet the while loop's condition, you end up here, outside the while loop
print('Done.')

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第一行user_num = 9作为用户的第一个输入。您希望这个数字满足while循环的条件，以便它在其中执行语句。
下面是一个很好的开始while循环的地方：https://www.w3schools.com/python/python_while_loops.asp

这是正确答案：

while user_num >=0:

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