Explanation:

- The "rule of election" relates to the principle that a person cannot both approbate and reprobate, i.e., accept and reject the same instrument or transaction.

- Lord Justice Lopez explained the rule of election clearly in the case Rendell v Pen.

- Option 1: Cavendish v Dacre – Not related to the rule of election.

- Option 2: Dalton v Fitzgerald – Not the case where Lord Justice Lopez stated the rule of election.

- Option 3: Rendell v Pen – This is the correct answer. Lord Justice Lopez explained the rule of election in this case.

- Option 4: Den v Slaiter – Not connected to the rule in question.