1- The relationship is:
classification and type.
"Difference" is how you classify or categorize what happens between two words or ideas. What kind or type of difference is it? "Opposite". For example, what is the relationship between the adjectives "happy" and "sad"? difference. What type of difference? "happy" is the opposite of "sad" and vice-versa.
2- The analogy goes like this:
police officer:patrol car/ dentist: drill
We are talking about certain tools the professionals mentioned need in order to perform their jobs.
3- The analogy goes like this:
photograph:memory/ recipe: food
A photograph makes a memory come to life, and a recipe is necessary to make food come to life.
4- The analogy goes like this:
Romeo and Juliet: drama/ Happy Birthday to You: music
.
"Romeo and Juliet" is a play. Thus, it belongs to the drama category (art).
"Happy Birthday to You" is a song. Thus, it belongs to the music category (art).