What or Which?

Dear Readers,

In the French language, one cannot use interchangeably the interrogatives "What...?" and "Which...?"
What? asks for either a definition or for an answer that is a direct object.  For example:  "What is a barracuda?  A fish or a mammal?"  and  "What are you eating?  I'm eating an apple."
Which is asked when there is a choice of answers.  For example:  "Which pair of shoes do you prefer?" and "Which is the correct answer, A or B?"
I find it interesting that in the English language people often do use these terms interchangeably.
See the examples below and try to imagine the word Which being used instead of What.

Example:  In an old "Seinfeld" episode, George is working on a project for the Mets that he is clueless about.  He is told to go down to the payroll office where he tells the clerk, "I'm working on the project."  The clerk asks, "What project?"

Example:  During an episode of "Hawaii 5-0," Commander Steve McGarrett has an investigator tailing his mother who walks into a grocery store.  She confronts the P.I. and asks, "Were you gonna ask my help in deciding what cantaloupes are ripe?"

Example:  Detective Danny Reagan on TV's "Blue Bloods," wants to protect a young woman that he has arrested and asks that she be transferred to protective custody. He's told that she's in the hospital.  He inquires, "What hospital?"

Example:  On the TV show "The Following," two followers of the serial killer Joe Carroll are discussing Emma, a third follower.  One guy says to the other, "I don't get the Emma you get."  Emma walks in on their conversations and asks, "What Emma is that?"

Example:  Songwriting duo Gunnar and Scarlette, on the TV show "Nashville," are told by their manager that they have officially received an offer to put one of their songs on hold.  Gunnar asks, "What song?"

Example:  In the novel Curse of the Spellmans by Lisa Lutz, Private Investigator Isabel Spellman is asked by her teen-aged sister Rae, "So is it all right if I go over to my friend's house?"  Isabel asks,
"What friend?"

Now read one example of the better word being used:

On an episode of BBC America's show "Copper," former Union army major and current New York businessman Robert Morehouse is at a meeting with some cronies.  He says, "Shall we take a recess from business?  The neighborhood is afire with whispers of last month's scandal."  One of the men asks, "Christ, which scandal?"  *Ah, leave it to the British to speak good English.

So, dear Readers, which blog will you refer to when faced with the What/Which dilemma?
I hope it's mine.