In Which of the Following Would the Title Pass to the Buyer

In which of the following would the title pass to the buyer only when the goods were "unconditionally appropriated" with assent?

A) Mark chose a guitar advertised in the catalogue of Guitars Galore Ltd., called the store, and after some discussion on its features and price, ordered it.
B) Jenny wanted amplifier A for her guitar, but the store only had amplifier B. She decided to take it because she wanted one right away.
C) Homer chose a guitar that was ready and he agreed to buy it. They had agreed that he could pay for it next month and pick it up when he paid.
D) Jethro chose the guitar and paid for it, but it had to be strung before it was ready.
E) After some discussion with the owner of Guitars Galore Ltd. as to which of the guitars there were best for a beginner, Bob bought a guitar for his son "on approval" and took it with him.