Answer:
1. Jews ⇒ d. Matthew
The Gospel according to Matthew is the first book of the New Testament in the Bible and seems to have been written for a Jewish audience. This is why the book included prophecies and stories from the Old Testament which Jews would be expected to know.
2. Greeks ⇒ a. Luke
The Gospel according to Luke is said to be intellectual in nature. It showed Jesus to be a divine being who was perfect in his ways and spoke with brilliance and eloquence. This is what the Greeks liked at the time and so it is said that this Gospel was aimed at them.
3. Romans ⇒ c. Mark
The Gospel according to Mark tried to explain the Jewish customs and the miracles performed by Jesus. This means that it was not written for those who already knew the ways of the Jews and considering that Israel was under Roman occupation at the time, it was most probably for Roman subjects.
4. All men ⇒ b. John
The Gospel according to John was written as a first-hand account by somebody who was with Jesus and loved him dearly. He wanted people to see that Jesus cared about everyone whether Jew or Gentile which means therefore, that he wrote for all men.