When you want your Python program to collect elements for a list at runtime, a. you use the append () to create the list and the list () method to populate it with input b. the only tricky part is knowing when to begin appending values c. you can use a known length or a sentinel value to signal completion of the list input d. you can use a for-loop but not a while-loop to populate the list with input values What Python statement(s) should be placed in the blank in order to collect user input to control the following loop? print ("Time for free ice cream!") for i in range (scoops): print ("Serving one scoop.") a. 1 = int (input ("How thany scoops today? ")) b. scoops - int (input ("How many scoops today? ")) c. print ("How many acoops today?") input 1 d. scoops - (input ("How many scoops today? "))