The Indemnity Principle Can Be Defined as Follows - Which

The indemnity principle can be defined as follows - which is correct?

A) If there is any doubt whether the costs have been reasonably incurred and are reasonable in amount, then the doubt will be resolved in favour of the paying party.
B) The winning party cannot recover more costs from his opponent than he has paid to his own solicitor.
C) In a claim where there are two Defendants either Defendant is permitted to seek an indemnity from the other if thought appropriate.
D) The Claimant on discontinuance of his claim against the Defendant will indemnify him in respect of his costs.