Teacher : What's wrong with this sentence? "Ann didn't go to the libary as she 'had had' a birthday."
Student : If the sentence which had 'had had' had had 'had', it would have been correct.
had = past tense of 'have'
'had had' = incorrect usage in teacher's statement
had had = past perfect tense of 'have'
'had' = the should-be correct usage