How do I set up a while loop to test for more than 1 variable

[danl]

errorType = raw_input("Please enter A or B or C as the Error Type: ")
while errorType != "A":
        print "Not valid"               
        errorType = raw_input("Please enter a valid Error Type ")

This works but I want the loop to check for != "B" and != "C" also.

How do I set it up to do this as I am very new to Python.

[bvdet]

while True:
    errorType = raw_input("Please enter A or B or C as the Error Type: ")
    if errorType.upper() in ('A', 'B', 'C'):
        break
    else:
        print "Invalid entry. Valid responses are 'A', 'B', and 'C'"

[danl]

Thank you, It is so obvious now.