Final answer:
DECS Department Order No. 25, s. 1974 requires the use of Filipino as the medium of instruction in all subjects in the elementary and secondary levels.
Step-by-step explanation:
DECS Department Order No. 25, s. 1974 requires the use of Filipino as the medium of instruction in All subjects in the elementary and secondary levels. This means that all subjects, including Mathematics, History, English, Biology, Chemistry, Physics, Social Studies, and more, should be taught using Filipino as the primary language of communication.