Read this and answer the question. If the question is unanswerable, say "unanswerable".

The 19th-century Liberal Prime Minister William Ewart Gladstone considered Burke "a magazine of wisdom on Ireland and America" and in his diary recorded: "Made many extracts from Burke—sometimes almost divine". The Radical MP and anti-Corn Law activist Richard Cobden often praised Burke's Thoughts and Details on Scarcity. The Liberal historian Lord Acton considered Burke one of the three greatest Liberals, along with William Gladstone and Thomas Babington Macaulay. Lord Macaulay recorded in his diary: "I have now finished reading again most of Burke's works. Admirable! The greatest man since Milton". The Gladstonian Liberal MP John Morley published two books on Burke (including a biography) and was influenced by Burke, including his views on prejudice. The Cobdenite Radical Francis Hirst thought Burke deserved "a place among English libertarians, even though of all lovers of liberty and of all reformers he was the most conservative, the least abstract, always anxious to preserve and renovate rather than to innovate. In politics he resembled the modern architect who would restore an old house instead of pulling it down to construct a new one on the site". Burke's Reflections on the Revolution in France was controversial at the time of its publication, but after his death, it was to become his best known and most influential work, and a manifesto for Conservative thinking.

How many books did Lord Acton publish on Burke?
unanswerable