What is the difference between a valid deductive argument and a fallacy?

Sarah tried to erase the files full of illegal in her computer before the police arrived, but she was too late.

Which sentence in this excerpt from leo tolstoy’s the death of ivan ilyich suggests that ivan ilyich felt his family and friends didn’t understand him and neglected him?

What is the meaning of "full tide" as it is used in this sentence? before i could explain to her the differences of language in this world, she was embarked on the full tide of another subject. a long and involved argument an inaccurate representation a detailed and lively discussion an uncontrollable flood