Before 008, the average oil production rate of newly cultivated soybean varieties in China was still lower than that of soybeans originally produced in a certain country, but from March 2008 to April 2010, the average oil production rate was greatly improved by scientific and technical personnel So far, although the average oil production rate has not improved any more, the gap between the average oil production rate of soybeans imported from a certain country is narrowing. Based on the above conclusions, which one must be correct? ['The average soybean oil production rate of a country imported from April 2010 has gradually decreased.', 'The average oil production rate of newly cultivated indigenous soybeans has gradually decreased since April 2010.', 'The average oil yield of native soybeans cultivated after April 2010 is higher than that of soybeans imported from a country during the same period.', 'The average soybean oil production rate of a country imported before 2008 is higher than that imported after April 2010.']