The correct answer is A) his testimony.
The evidence that Joaquin has to support his version of the facts is his testimony.
Joaquin as a plumber has to double-check or triple-check his work before he is gone. His reputation is above all. But in this case, evidence that he has to support his version of the facts is his testimony. Owen should have asked Joaquin the kind of work he did, check it directly making the necessaries revisions, and ask for a guarantee in case the work was not done properly.
The other options of the question were B) Joaquin's testimony. C) None. D) Faulty work is a breach of the contract. E) Joaquin is liable for faulty workmanship.