In the classroom
A teacher said, "Mary, I'd like you to give me a sentence beginning with 'I', please."
Mary thought for a few seconds and then said, "I is..."
The teacher interrupted her and said, "No Mary, you cannot begin a sentence with 'I is' - you must use 'I am'."
Mary looked upset and said, "But Miss..."
The teacher shouted, "Give me a sentence beginning with 'I am', please."
Mary shrugged her shoulders and said, "I am the ninth letter of the alphabet."