Question: Longest and most expensive trial in us history?
Answer: McMartin preschool trial
Disambiguated questions and answers: question: Longest and most expensive trial in us history when the trial ended in 1990?
Longest and most expensive trial in us history when it took place in 1917?
answer: McMartin preschool trial
Hindu–German Conspiracy Trial
Natural Questions answer: The McMartin preschool trial (from the Wikipedia article "McMartin preschool trial")