Final answer:
The phrase that best fills the blank is 'mayor que', meaning 'older than'. Maria is older than Carmen by four years.
Step-by-step explanation:
The phrase that best fills the blank in the sentence is mayor que, which means 'older than' in English. So, the sentence translates to: Maria is older than Carmen. This phrase indicates that Maria is older than Carmen by four years.
Learn more about Comparisons of age in Spanish