The Malbec grape, originally grown in France, has become the main varietal in Argentina. This is surprising because most Malbec grown in Argentina is grown at high altitudes, whereas the Malbec grape once was grown at low altitudes. Ttherefore, Argentinian winegrowers should grow the Malbec grape at low elevations. Which of the following, if true, would most weaken the conclusion of the argument? ['The Malbec vine is susceptible to phylloxera, a plant louse that only grows at low altitudes.', 'Some varietals are unable to grow at high altitudes.', 'Malbec has recently enjoyed a surge in popularity, and can be found in many different countries.', "The soil at high altitudes is filled with nutrients that help many of Argentina's varietals flourish."]