Teacher's Nightmare!

Got these from someone through email and like to share them here...

TEACHER:  "Harold, what do you call a person who keeps on talking when people are no longer interested?"

HAROLD:     "A teacher."

TEACHER:  "Winnie, name one important thing we have today that we didn't have ten years ago?" 

WINNIE:        "Me!"

TEACHER:   "Donald, what is the chemical formula for water?"
DONALD:     "H I J K L M N O." 

TEACHER:  "What are you talking about?"
DONALD:     "Yesterday you said it's H to O."

TEACHER:  "Glenn, how do you spell 'crocodile?' "
GLENN:       "K-R-O-K-O-D-I-A-L"
TEACHER:  "No, that's wrong"
GLENN:       "Maybe it is wrong, but you asked me how I spell it."  

TEACHER:  "John, why are you doing your math multiplication on the floor?"

JOHN:          "You told me to do it without using tables."

TEACHER:  "Maria, go to the map and find North America."
MARIA:         "Here it is."
TEACHER:  "Correct.  Now class, who discovered America?"
CLASS:        "Maria."