The multiple cropping index refers to the ratio of the total sown area of crops to the area of arable land within a year, and is generally expressed as a percentage. The level of the multiple cropping index is limited by local conditions such as soil, water conservancy, fertilizer, labor, and scientific and technological levels. A long frost-free period, sufficient water, and reasonable interplanting are the basis for improving the multiple cropping index. Based on the above definition, which of the following statements about multiple indices is correct? ["China's south to north, the regional multiple cropping index has gradually increased.", 'the multiple crop index is closely related to the longitude of the region.', 'the multiple crop index in spring and autumn is higher than in summer and winter.', 'the higher level of agricultural science and technology, but the multiple crop index exceeds 100%.']