During the Second World War, merchant ships sailing on the ocean were often attacked by bombers, and many merchant ships had erected anti-aircraft guns on the ships. However, commercial ships swayed more severely at sea, and it was difficult to hit the aircraft with anti-aircraft guns After the war, researchers found that from the statistics of commercial ships that had erected anti-aircraft guns throughout the war, the shooting rate of downing enemy aircraft was only 4%. Therefore, the researchers believe that the anti-aircraft guns on commercial ships are worth more. Which of the following, if true, would most weaken the researchers' conclusions? ['During the war, the proportion of commercial vessels without anti-aircraft guns being sunk was as high as 25%; while the proportion of commercial vessels with anti-aircraft guns being sunk was less than 10%.', 'Merchant ships with anti-aircraft guns may scare them away in some cases even if they cannot hit them.', 'The cost of setting up the anti-aircraft gun is a big investment, and after the war, in order to operate efficiently, it will take another fund to dismantle the anti-aircraft gun.', 'Generally speaking, the cost of the above merchant ships for anti-aircraft guns only accounts for a very small part of the total value of the entire merchant ship.']