Final answer:
The correct conjunction to complete the sentence is 'pero'. It is used to express contrast or contradiction in Spanish sentences.
Step-by-step explanation:
The correct conjunction to complete the sentence is pero. "No todos los suplementos se publican todos los días pero salen una vez cada semana" translates to "Not all supplements are published every day but come out once a week." This conjunction is used to express contrast or contradiction between the first and second part of the sentence.
Learn more about Spanish conjunctions