All the listed options are actually considered low-acid fruits. Blueberries, huckleberries, strawberries (pH 3.1-3.7), cherries (pH 3.2-4.0), sweet peaches (pH 3.3-4.0), sweet plums (pH 3.8-4.0), mangoes (pH 3.9-4.6), and elderberries all have relatively higher pH values compared to highly acidic fruits like lemons or grapefruits. Therefore 'All of these' is correct.