In Royal Bank of Scotland Plc V

In Royal Bank of Scotland plc v. Etridge (No 2) (2001) , Lord Nicholls said that the question is whether the transaction is 'not readily explicable by the parties' relationship'. Which of the following statements is true?

A) It is unnecessary to show that a transaction calls for an explanation when asking the court to infer (presumed) undue influence.
B) The complainant must show that the transaction calls for an explanation if he wants the court to find overt (actual) undue influence.
C) A transaction calls for an explanation only if the values exchanged deviate from the market price.
D) Whether a transaction calls for an explanation depends on the nature of the parties' relationship, the nature of the transaction, the impact of the transaction on the complainant, and on the latter's ability to provide for others in a close relationship to him.